PHYS165 / PHYS 165 Module 3: (Latest Update 2026 / 2027) Physics | Questions, Answers & Review Material | Grade A | 100% Correct - Portage Learning

PHYS165 / PHYS 165 Module 3: (Latest Update 2026 / 2027) Physics | Questions, Answers & Review Material | Grade A | 100% Correct - Portage Learning 2026 / 2027 Academic Year Q: What is the branch of classical mechanics concerned with the study of forces and their effects on motion called? Answer: Dynamics Q: Which of the following is the BEST description of a force? a) simply a push or a pull b) an action exerted on an object which may change the object's state of rest or motion c) something only found in sci-fi movies d) A and B Answer: a) simply a push or a pull b) an action exerted on an object which may change the object's state of rest or motion c) something only found in sci-fi movies d) A and B Q: What is the unit for force? Answer: Newtons Q: In a free body diagram of a box resting on the floor, how many forces would you draw? A) 1 B) 2 C) 3 D) 4 Answer: B) 2 Q: What is the specific, immediate, identifiable cause of a force called? Answer: Agent of Force Q: When a baseball player hits a home run, what is the agent of the force applied to the ball? Answer: The bat Q: What makes a field force different from a contact force when it comes to agents and receivers of forces? Answer: In field forces the agent and receiver of the force do not have to touch, but in contact forces the agent and receiver of the force must touch Q: A force exerted from any surface (the agent) onto an object that is pressing against the given surface is known as a(n) _______. A) Normal Force B) Tension Force C) Elastic Force D) Field Force Answer: A) Normal Force Q: Q: The force that acts on an object to resist motion is known as ______________. A) Normal B) Friction C) Inertia D) Contact Answer: B) Friction Q: The resistive force that occurs when the two surfaces do slide across each other is known as ____________________________. A) Static Friction B) Kinetic Friction A) Static Friction: starting Answer: B) Kinetic Friction: sliding Q: What is the definition of inertia? Answer: Inertia is the property of an object which resists any change in the object's motion Q: Law of Inertia? Answer: An object at rest remains at rest and an object in motion stays in motion unless acted on by a net outside force Q: Which of the following is a description of acceleration according to Newton's Second Law of Motion? Acceleration _________. Answer: Is directly proportional to the net force acting on the system Q: Acceleration of an object is directly proportional to the net external force acting on an object Answer: Acceleration of an object is inversely proportional to the mass of the object Acceleration of the object is in the same direction as the net external force Q: Law of Interaction? Answer: For every action, there is an equal but opposite reaction Q: According to Newton's Third Law of Motion, what is the reaction to a ball being kicked by a teenager? Answer: The ball applies a force to the teenager's foot Q: True or False: In physics. The Weight and Mass of an object have the same value. Answer: False Q: What is the weight of a 1560 kg car? Answer: W=mg 1560 x 9.80= 15,288 15,290 N Q: When a tugboat pulls a barge with a net force of 842,000 N, what acceleration will the barge experience if it has a mass of 1,625,000 kg? Answer: Use f=ma revise a=Fnet/m 842,000/ 1,625,000 = 0. 0.518 m/s^2 Q: When a 2270 kg car accelerates from rest to 12.0 ms in 2.50 s, what net force acts on the car during this time? Answer: Use a=vf-vi/t answer in m/s^2 Use f=ma answer in N (12.0 - 0 ) / 2.50 = 4.80 2270 * 4.80 = 10,896 10,900 N Q: Calculate the spring constant of a spring if it stretches 17.5 cm when a force of 102 N acts on it. Answer: use k=f/x 102/ 17.5= 5.82 N/m Q: What do physicists call the resistance to motion or attempted motion? Answer: Friction, drag or air resistance Q: Which of the following statements best describes surface friction? Answer: When a person slides a crate across the floor and the crate does not move, the crate has kinetic friction acting on it. Q: When a person tries to move a crate by pushing it, and it does not move, the crate has static Answer: friction acting on it Q: A factory worker is pushing horizontally on a 92.0-kg wooden create that is sitting at rest on a wooden horizontal floor. The coefficient of static friction between the crate and the floor is 0.500 and the coefficient of kinetic friction between the crate and the floor is 0.300. Answer the following questions about this scenario. A) What is the weight of the crate? B) What is the maximum static friction force that can act on the crate? C) What is the kinetic friction force that could act on the crate? D) When the factory worker pushes with 635 N, what is the net force acting on the crate? E) When the factory worker pushes with 635 N, what is the acceleration of the crate? Answer: a) W=mg Answer in N W= 92.0 x 9.80 = 901.6 = 902 N b) Fs= us x N 0. 500 x 902= 451 N c) Fk= uK x N 0.300 x 902= 271 N d) Fnet =Fa- Fk 635 - 271 = 364 N e) a= Fnet/ m 364N/ 92.0kg= 3.96 m/s^2 Q: True or False: When an object is in uniform circular motion its velocity is constant. Answer: False Q: A 38.4-kg child is playing on a Merry-Go-Round that has a diameter of 3.42 m. She is moving at a uniform tangential speed of 3.32 . Answer the following questions about the child's motion. A) Calculate the centripetal acceleration of the child. B) Calculate the centripetal force acting on the child. A) aC= V^2/ r aC= 3.32^2 / 1.71 aC= 6.4458 6.45 m/s ^2 b) Fc= mv^2 Fc= (38.4) (3.32^2)/ 1.71 Fc= 247.5 248 N* Which of the following is true according to Newton's Universal Law of Gravitation? Answer: Gravitational forces are felt between any two masses. What is the gravitational force between two identical trucks of 19,030 kg separated by 31.00 m? Answer: Fg=Gm1 x m2/d^2 Fg= 6.673x10^-11 x (19,030) x (19,030) / 31.00^2 2.51x10^-5 Fg= 2.51x10^-5N What are the four Fundamental Forces of Nature? Gravitational Electromagnetic Calculate the acceleration due to gravity on the surface of Mercury, given that its mass is 3.18 x 1023 kg and its average radius is 2.43 x 106 m. Use g=Gm/d^2 g= (6.673x10^-11) x (3.18x10^23) / (2.43x10^6)^2 g= 3.59 m/s^2 The mass of Jupiter is 1.90 x 1027 kg and its average distance from the Sun is 7.78 x 1011 m. If the gravitational force of attraction between the Sun and Jupiter is 4.17 x 1023 N, what is the mass of the Sun? Use Fg=Gm1m2/d^2 Solve for m1 G=6.673x10^-11Nm^2/kg^2 Answer in kg Weak Nuclear Force Strong Nuclear Force What is the branch of classical mechanics concerned with the study of forces and their effects on motion called? Dynamics Which of the following is the BEST description of a force? a) simply a push or a pull b) an action exerted on an object which may change the object's state of rest or motion c) something only found in sci-fi movies d) A and B Answer A and B What is the unit for force? Newtons What is the specific, immediate, identifiable cause of a force called? Agent of Force Draw a Free Body Diagram of a picture resting on a shelf. Then answer the following questions about your free body diagram: When a baseball player hits a home run, what is the agent of the force applied to the ball? The bat What makes a field force different from a contact force when it comes to agents and receivers of forces? In field forces the agent and receiver of the force do not have to touch, but in contact forces the agent and receiver of the force must touch a. How many forces are in your diagram?1. 1 2. 2 3. 3 4. 4 b. In which direction does the shelf apply a force on the picture?1. Upward2. Downward3. There is not enough information to determine the direction 4. The table does not apply a force to the laptop c. How does the magnitude of the weight of the picture compare to the magnitude of the normal force acting on the picture? 1. The weight of the picture is larger than the normal force acting on the picture 2. The normal force acting on the picture is larger than the weight of the picture 3. Both the normal force and the weight of the picture have the same magnitude 4. There is not enough information to compare the magnitude of these forces. a) 2 b) 1 c) 3 Draw a Free Body Diagram of a crate being pushed horizontally across a horizontal floor by a person at a constant speed. Then answer the following questions about your free body diagram: a. How many forces are in your Free Body Diagram?1. 12. 23. 34. 4 b. How does the magnitude of the crate's weight compare to the magnitude of the normal force acting on the crate? 1. The weight of the crate is larger than the normal force acting on the crate 2. The normal force acting on the crate is larger than the weight of the crate 3. The magnitudes of these forces are the same 4. There is not enough information to compare the magnitudes of these forces c. How does the magnitude of the force applied by the person onto the crate compare to the magnitude of the frictional force acting on the crate? 1. The force applied by the person is larger than the frictional force acting on the crate. 2. The frictional force acting on the crate is larger than the force applied by the person 3. The magnitudes of these forces are the same 4. There is not enough information to compare the magnitudes of these forces. a) 4 b) 3 c) 3 d) 5 Draw a Free Body Diagram of a car coasting to the right across a level road and slowing down. Then answer the following questions about your free body diagram: a. How many forces are in your Free Body Diagram?1. 1 2. 2 3. 3 4. 4 b. How does the magnitude of the car's weight compare to the magnitude of the normal force acting on the car? 1. The weight of the car is larger than the normal force acting on the car 2. The normal force acting on the car is larger than the weight of the car 3. The magnitudes of these forces are the same 4. There is not enough information to compare the magnitudes of these forces c. How does the magnitude of the net force acting on the car compare to the magnitude of the frictional force applied onto the car? 1. The net force acting on the car is larger than the frictional force acting on the car. 2. The frictional force acting on the car is larger than the net force acting on the car 3. The magnitudes of these forces are the same 4. There is not enough information to compare the magnitudes of these forces. a) 3 b) 3 c) 3 What is the definition of inertia? Inertia is the property of an object which resists any change in the object's motion Which one of the following statements is NOT part of the Law of Inertia? For every action, there is an equal but opposite reaction Which of the following is a description of acceleration according to Newton's Second Law of Motion? Acceleration _________. Is directly proportional to the net force acting on the system Which of the following is NOT true about actions and reactions according to the Law of Interaction? Actions and reactions act on the same system According to Newton's Third Law of Motion, what is the reaction to a ball being kicked by a teenager? The ball applies a force to the teenager's foot True or False: In physics. The Weight and Mass of an object have the same value. False What is the weight of a 1560 kg car? W=mg Answer in N When a tugboat pulls a barge with a net force of 842,000 N, what acceleration will the barge experience if it has a mass of 1,625,000 kg? Use f=ma revise so that a=Fnet/m answer in m/s^2 When a 2270 kg car accelerates from rest to 12.0 ms in 2.50 s, what net force acts on the car during this time? Use a=vf-vi/t answer in m/s^2 Use f=ma answer in N Calculate the spring constant of a spring if it stretches 17.5 cm when a force of 102 N acts on it. use k=f/x Answer in N/m What do physicists call the resistance to motion or attempted motion? Friction, drag or air resistance Which of the following statements best describes surface friction? When a person slides a crate across the floor and the crate does not move, the crate has kinetic friction acting on it. When a person tries to move a crate by pushing it, and it does not move, the crate has static friction acting on it A factory worker is pushing horizontally on a 125 kg wooden create which is sitting at rest on a wooden horizontal floor. The coefficient of static friction between the crate and the floor is 0.500 and the coefficient of kinetic friction between the crate and the floor is 0.300. Answer the following questions about this scenario. a. What is the weight of the crate? b. What equation could be used to find the weight of the crate? No equation is needed, the weight is given. W = mg F = ma Fs max=μsN c. What is the maximum static friction force that can act on the crate? d. Which equation could be used to find the maximum static friction force? Fkmax=μkN Fsmax=μsN F = ma W = mg e. What is the kinetic friction force that could act on the crate? f. Which equation could be used to find the kinetic friction force acting on the crate? Fk=μkN Fs=μsN F = ma W = mg g. When the factory worker pushes with 495 N what is the net force acting on the crate? h. When the factory worker pushes with 495 N what equation can be used to find the net force acting on the crate? Fnet=ma Fnet=Fa Fnet=Fa−Fk Fnet= 0 since the forces are balanced i. When the factory worker pushes with 495 N what is the acceleration of the crate? 3.96 ms2 9.80 ms2 1.02 ms2 0 since the maximum static friction force is greater than the force applied j. When the factory worker pushes with 727 N what is the net force acting on the crate? k. When the factory worker pushes with 727 N what equation can be used to find the net force acting on the crate? Fnet=ma Fnet=Fa Fnet=Fa−Fk Fnet= 0 since the forces are balanced l. When the factory worker pushes with 727 N what is the acceleration of the crate? 5.82 ms2 9.80 ms2 2.89 ms2 0.916 ms2 a) W=mg Answer in N b) 2 c) FsMax=mewsN Answer in N d) 2 e) Fk=mewkN answer in N f) 1 g) 0 h) 4 i) 4 j) Fnet=Fa=Fk answer in N k) 3 l) 3 True or False: When an object is in uniform circular motion its velocity is constant. False A 38.4-kg child is playing on a Merry-Go-Round that has a diameter of 3.42 m. She is moving at a uniform tangential speed of 3.32 ms. Answer the following questions about the child's motion. a. Calculate the centripetal acceleration of the child. b. Which equation is the best choice to calculate the centripetal acceleration of the child? Fc=mv2r ac=v2r Fnet=ma W = mg c. Calculate the centripetal force acting on the child. d. What equation is the best choice to calculate the centripetal force acting on the child? Fc=mv2r ac=v2r Fnet=ma W = mg a) ac=v^2/r answer in m/s^2 b) 2 c) Fc=mv^2/r Answer in N d) either 2 or 3 Which of the following is true according to Newton's Universal Law of Gravitation? Gravitational forces are felt between any two masses. What is the gravitational force between two identical trucks of 15,030 kg separated by 35.00 m? Use Fg=Gm1m2/d^2 Answer in N Calculate the acceleration due to gravity on the surface of Saturn, given that its mass is 5.68 x 1026 kg and its average radius is 5.85 x 107 m. Use g=Gm/d^2 Answer in m/s^2 The mass of Jupiter is 1.90 x 1027 kg and its average distance from the Sun is 7.78 x 1011 m. If the gravitational force of attraction between the Sun and Jupiter is 4.17 x 1023 N, what is the mass of the Sun? Use Fg=Gm1m2/d^2 Solve for m1 G=6.673x10^-11Nm^2/kg^2 Answer in kg What are the four Fundamental Forces of Nature? Gravitational Electromagnetic Weak Nuclear Force Strong Nuclear Force Dynamics the study of forces and their effects on motion Force any action that could change an object's state of motion. (simple def: any kind of push or pull on an object. ) Is a force required to keep an object moving? No (a force is only required to change motion, not maintain constant velocity) Is force a vector or a scalar? Vector, it has magnitude and direction (The harder a force is applied, the larger the magnitude) If all forces are balanced in all directions, then the object's motion or rest WILL OR WILL NOT change? will not change What is the agent of a force ? the specific, immediate, and identifiable cause of a force Can a force exist without an agent? No Forces are measured in.... Newton (N) Two types of forces Contact forces and field forces Contact forces Forces that are touching the object Ex: tension in a rope, buoyancy, friction, pushing, pulling, hitting/kicking Field force Forces that are not touching the object ex: gravity, magnetism, electric force What types are these forces: 1. Magnetism 2. Tension in a rope 3. Buoyancy 4. Friction 5. Gravity 1. Field 2. Contact 3. Contact 4. Contact 5. Field The unit of force Derived unit 1N = 1kg-m/s^2 (1N = 1/4 pound = 1/2 cup of water ) System the object (or group of objects) being analyzed. (a model of a real world situation that is either the object of concern or a collection of objects of concern ) What are the two types of systems in physics? Open and closed Open system A system with forces acting on it from outside agents Closed system a system with no forces acting on it from outside agents (key idea: outside versus inside agents) Free Body Diagram a diagram showing all the forces acting on an particle representing an object A free body diagram has only: - a point representing the system - all the external forces acting on the system - the acceleration What is not included on a free body diagram? -the surroundings -forces where the system is the agent How are the forces labeled on a free body diagram? Using the agent on system format (ex: force of earth on car) Newton's First Law An object at rest remains at rest, and an object in motion remains in motion, unless acted on by a net outside force. Net external force the vector sum of all forces acting on an object that have agents that are outside of the system When is acceleration zero? When the net external force is zero Inertia the property of an object that resists any change in its motion, neither in terms of speed nor direction Newton's 2nd Law F = ma - The acceleration of an object is directly proportional to the net force of an object - The acceleration of an object is inversely proportional to the mass of an object - The acceleration of an object is in the same direction as the net force What is the equation for Newton's 2nd Law F=ma (Force = mass x acceleration) According to Newton's Second Law, what determines acceleration? - Magnitude of net force - Mass of the object - Direction of the net force Newton's Third Law Whenever an agent exerts a force on an object, the object exerts an equal force on the agent in the opposite direction. (For every action, there is an opposite and equal reaction) What evidence can you think of that shows that the Earth pulls on the Moon? The Earth pulls the moon into a circular orbit What evidence can you think of that shows that the Moon pulls on the Earth? The Moon pulls on the Earth causing tides Weight a field force caused by the gravitational pull of the Earth (also called the force of gravity or force of weight ) What is the agent of weight The entire Earth Formula for weight W = mg (W - the weight of an object in newtons; m - the mass of the object in kilograms, g is the acceleration d/t gravity) What symbols can represent weight? F^Earth on object=Fw=Fg=W What is the difference between mass and weight? Mass: amount of matter (kg), does NOT change Weight: gravitational force (N), DOES change with location Why do astronauts weigh less on the Moon but have the same mass? Gravity is weaker on the Moon, but the amount of matter stays the same. What causes tension, elastic and normal forces Cause by the atoms in solids interacting with each other by quantum springs If you try to pull atoms in a solid apart..... they attract each other If you try to push atoms in a solid together they repel each other Normal force a force exerted by an surface on an object pressing against it Why is the normal force called "normal" ? Because it is perpendicular to the surface Is the normal force always equal to weight? No. It depends on the situation (angles, acceleration, other forces). What symbol represents the normal force? N Tension A pulling force exerted by. a rope, wire or chain when they pull on objects What is the symbol and units for tension? T. Newtons Elasticity the ability of an object to return to its original size and shape after a distorting force is removed ex of elastic things: rubber bands, springs, skin, everything is elastic to some degree Hooke's Law of Elasticity the restoring force is directly proportional to the amount of deformation of an object Equation of elastic force F = -k(delta x) (k is the spring constant, units are N/m) Friction a force acting on an object that resists motion In what direction does friction act? Parallel to the surface and opposite the motion or attempted motion. Fluid friction a resistive force that occurs when an object moves through a fluid ex: air resistance, drag on a boat along a river Rolling friction a resistance friction that occurs when an object rolls across another object Surface friction A resistive force that happens when one object slides or tries to slide across another What are the two types of surface friction? Static (starting) and kinetic (sliding) Kinetic friction a resistive force that occurs when the two surfaces do slide across each other (the direction of the friction is OPPOSITE the direction of the velocity) Static friction a resistance force that occurs when one object attempts to slide across another object, but there is no relative motion (the direction of the friction is opposite the direction of the push) Which is larger: static or kinetic friction? Static friction is larger than kinetic friction Equation for kinetic friction Fk = μk(N) (kinetic friction = coefficient of kinetic friction X normal force; kinetic friction is proportional to the normal force) Equation for static friction Fsmax = μs(N) (maximum static friction = coefficient of static friction X normal force; maximum static friction is proportional to the normal force) What is the coefficient of friction (μ)? A number with no units that depends on the materials in contact. Does static friction always equal μₛN? No. It has a maximum value. Centripetal towards the center If speed is constant, the motion is ... Uniform Circular Motion Why is there acceleration in uniform circular motion? Because direction is constantly changing, even if speed is constant Uniform circular motion a model of motion for any object that is moving in a circle at a constant speed Centripetal force required to keep an object traveling in a circle Centripetal acceleration the net external force acting on an object in uniform circular motion Tangential speed a speed associated with circular motion that is directed along the tangent (edge) of the circle Centripetal acceleration equation ac = v^2/r Centripetal force equation Fnet =mv^2/r (comes from F=ma, aka Newton's Second Law of Motion) Is centrifugal force a real force? No, its a feeling d/t inertia, not a real force with an agent Newton's Universal Law of Gravitation The gravitational force between any two objects with mass Universal Law of Gravitation equation Fg=G(m1m2/d^2) Is gravitational force always attractive or repulsive? Always attractive What does each variable mean in Fg=G(m1m2/d^2) ? m1,m2 = masses (kg) d = distance between centers (m) G = gravitational constant Fg = gravitational force (N) G (universal gravitational constant) 6.673 x10^-11 Nm^2/kg^2 How are W=mg and the Universal Law of Gravitation related? Weight is the gravitational force between an object and Earth The Four Fundamental Forces of Nature 1. Gravitational 2. Electromagnetic 3. Strong Nuclear Force 4. Weak Nuclear Force Electromagnetic force force from electric charges and magnetism. All contact forces come from this (normal force, friction, tension, etc) Strong Nuclear Force an attractive force between the protons and neutrons in the nucleus of an atom Weak Nuclear Force Responsible for certain types of radioactive decay what is the branch of classical mechanics concerned with the study of forces and their effects on motion called? Dynamics what is the simple definition of a force? A push or a pull What is the more complex definition of a force? a force is an action exerted on an object that may change the motion of an object What is the unit for force, and what is its relationship to the fundamental units? Newtons (N); 1N=kgm/s2 What is an agent of a force? the specific, immediate, and identifiable cause of a force When a soccer player kicks a soccer ball, what is the agent of the force applied to the soccer ball? the players foot There are two kinds of forces. What are they? contact and field Differentiate between contact and field forces For contact forces, the agent and receiver of the force must touch; for field forces, no contact is needed Give an example of a contact force typing on a keyboard Give an example of a field force Magnetism, gravity, and electricity What are the parts of a free body diagram? You draw the object and all of the forces acting on the object What is the property of an object that resists any change in its motion? Inertia What is the other name of Newton's First Law of motion? Law of Inertia What is the other name Newton's Second Law of Motion? Law of Acceleration What is the other name of Newton's Third Law of Motion? Law of Interaction Which of the following statements is NOT part of Law on Inertia? For every action, there is an equal but opposite reaction Which of the following is NOT a description of acceleration according to Newton's Second Law of Motion? Is directly proportional to the velocity of the system Which of the following is NOT true actions and reactions according to the Law of Interaction? Actions and reaction act on the same system What is the equation associated with the Law of Acceleration? Fnet = ma What is the reaction to a person punching a desk? The desk applies a force to the person's hand What is the reaction to the gravity pulling down on a falling leaf? The leaf pulls up on the Earth Differentiate between weight and mass The weight of an object is a measure of the pull of gravity on that object, while the mass of an object is the measure of the amount of material in an object. What is the mathematical relationship between weight and mass W = mg What is the weight of a 91.3 kg ball? W = mg W = (0.0913 kg) (9.80 m/s2) W = 0.895 N What is the mass of a 954.6 kg elephant 954.6 kg What is the mass of a 282,000 N rocket? w = mg m = W/g m = 282000 N/9.80 m/s2 m = 28775.5 m = 28,800 kg When a model rocket is launched with a net force of 25.0 N, what acceleration will it experience if it has a mass of 35.0 g a = Fnet/m a = 25.0 N/0.035 kg a = 714 m/s2 If a 2696 kg car decelerates at 2.315 m/s2, what net force acts on it? Fnet = ma Fnet = (2696 kg)(2.315 m/s2) Fnet = 6241 N When a 15,700 kg truck accelerates from rest to 15.0 m/s in 12.50 s, what net force acts on the truck? a = Vf - Vi/t a = (15.0 m/s - 0 m/s) / 12.50 s a = 1.20 m/s2 Fnet = ma Fnet = (15700)(1.20 m/s2) Fnet = 18840 N Fnet = 18,800 N What is the general term for the force exerted on you by the chair you are sitting on? Normal force When walking your dog on a leash, what kind of force can you exert on him to keep him safe? Tension force Calculate the spring constant of a rubber band if it stretches 5.00 cm when a force of 3.55 N acts on it? F = kx k = F/x k = (3.55 N)/(0.0500 m) k = 71.0 N What is more elastic, the suspension springs in your car or a metal spoon? The suspension springs in your car What do physicists call the resistance to motion or attempted motion? Friction What do physicists call the resistance to any changes in an object's motion Inertia What are the two types of surface friction Static (starting) and Kinetic (sliding) How much force is needed to start a 68.4-kg skier on waxed wooden skis on wet snow? W = mg = 68.4 kg (9.80 m/s2) = 670.32 N Fk = MxN = 0.14 (670.32 N) = 93.8 N A ski instructor pushes a 68.4-kg skier on waxed wooden skis on wet snow. How much acceleration does the skier experience if he pushes with a 155-N horizontal force? W = mg = 68.4 kg (9.80 m/s2) = 670.32 N Fk = Mk N = 0.1 (670.32 N) = 67.032 N Delta x = Xf - Xi = 155 N - 67.032 N = 87.968 N Fnet = ma a = Fnet / m = 87.969 N / 68.4 kg = 1.29 m/s2 Which of the following is nOT true about an object in uniform circular motion? The velocity is constant A 49.5-kg child is playing on a Merry-Go-Round that has a diameter of 2.25 m. She is moving at a tangential speed of 5.32 . Calculate her centripetal force and her centripetal acceleration. Fc = mv2/r = (49.5 kg) (5.32 m/s)^2 / 1.125 m = 1250 N ac = v2 / r = (5.32 m/s) ^2 / 1.125 m = 25.2 m/s2 Which of the following is NOT true according to Newton's Universal Law of Gravitation? Gravitational forces can be both attractive and repulsive What is the gravitational force between two identical masses of 803 kg separated by 5.00 m? Fg = G (m1m2) / d2 = 6.673 x 10-11 (803)(803)/5.002 = 6.673 x 10-11 (25792.36) = 1.72 x 10-6m Calculate the acceleration due to gravity on the surface of Mars, given that its mass is 6.39 x 1023 kg and its average radius is 3.389 x 106 m. Fg = 6.673 x 10^-11 (6.39 x 10^23 / 3.389 x 10^6) = 3.71 m/s2 The mass of the Earth is 5.97 x 1024 kg and its average distance from the Sun is 1.496 x 1011 m. If the gravitational force of attraction between the Sun and the Earth is 3.54 x 1022 N, what is the mass of the Sun? Fg = G(m1m2/d2 ) m1 = Fgd2 /Gm2 = (3.54x1022 N)(1.496x1011 m)2 / (6.673x10-11) (5.97x1024 kg) = 1.99x1030 kg What are the four fundamental forces of nature? Gravity, electromagnetic force, Strong nucelar force, and Weak nuclear force Contact forces are an example of what kind of fundamental force? Electromagnetic Which two fundamental forces act only on an atomic scale? Strong nuclear force, weak nuclear force.