AQA GCSE Physics -Paper 2 SOLUTIONS 100% CORRECT GRADE A+ GUARANTEED

Scalar quantities with only magnitude such as speed, distance, time and mass. Vector quantities with a magnitude and direction e.g. acceleration, force momentum and weight. A vector quantity can be represented as an arrow, the size representing the magnitude and the direction, the direction. Non-contact force the objects are physically separate e.g. magnetism/gravity/electrostatic. 3 non-contact forces magnetism gravity electrostatic Contact force objects are physically touching . 3 contact forces friction resistance tension Gravity Weight is the force acting on an object due to gravity, it acts on an objects 'centre of mass' and is directly proportional to mass Weigh Equation Weight = mass x grav. field strength Resultant forces A number of forces acting on an object may be replaced by a single force that has the same effect as all the original forces acting together, this single force is the called the resultant force. In a tug of war, 1000N to the left and 800N to the right. The resultant force is 200N to the left Free-Body force diagrams When an object is acted on by more than one force you can draw a free-body force diagram to work out the resultant force on the object. It shows the forces acting on an object without any other objects or other forces shown. Each force is shown on the diagram by a vector, which is an arrow pointing in the direction of the force. ( the normal force is that component of the contact force that is perpendicular to the surface that an object contacts) How to resolve forces (force diagram steps) 1. Decide on a scale of N per cm. 2. Draw the 2 given forces, giving respect to their length (more cm if more N) and the angle that you are given 3. Draw a line connecting the end of the 2 other lines to form a triangle 4. Measure the length of this line, then convert it to N by using the scale Relationship between Joules and work done When a force causes and object to move, work is done on the object so when the force causes displacement. One joule of work is done when a force of 1 newton displaces an object 1 metre. 1 Joule = 1 newton-metre. Equation for word done work done = force x distance Elastic Deformation When an elastic object is stretched, bent, twisted or compressed it will return to its original form Inelastic Deformation Polyethene bags will not return to their original shape after being deformed, this is inelastic. Hooke's Law The extension of an elastic object is directly proportional to the force applied as long as the limit of proportionality is not exceeded: Equation for force (Hooke's law) force = spring constant x extention Extension and compression's relationship with elastic potential energy explanation A force that stretches or compresses a spring does work and elastic potential energy is stored in the spring, provided the spring is not elastically deformed, the work done and elastic potential energy are equal. Before the limit of proportionality is breeched the relationship is linear (directly proportional) afterwards it is non-linear Elastic potential energy equation (given) Elastic potential energy = 1/2 x spring constant x extension^2 Moment meaning The turning effect of a force is called its 'moment' Moment equation moment = force x distance Balancing If an object is balanced the clockwise moment is equal to the anticlockwise moment. Levers A lever consists of a load, effort and pivot, levers use moments to multiply a force, they allow a larger force to act on the load that is supplied by the effort. Engine Gears Engine gears have two main jobs, producing torque and speed, however they are inversely proportional so gears are made to make a compromise between the two in any given situation. When starting a car we want high torque, which means being able to carry a greater load , and consequentially less speed. In low gears this is achieved as... 1. The engine causes a small cog on the engine axle to rotate. 2. The small cog on the engine axle is connected to a larger cog on the wheel axle, which increases the torque (moment) exerted. 3.A high turning force but low speed is exerted on the wheel (low gear) When a car is already moving, we want a high speed which is achieved as... 1.The engine causes a larger cog on the engine axle to turn. 2.The larger cog on the engine axle is connected to a smaller cog on the wheel axle, causing a high rate of rotation, but a low turning force. 3. The wheel rotates quickly, causing a high speed Unit for pressure Pressure is a measure of force per unit of area, the si unit is Pascals (Pa) which is one N/m^2 Pressure Equation Pressure = force normal to the surface/area Manometer with oil and water The pressure is equal at each end of the tube, so the less dense oil is higher.(p=hdg)(on sheet) Buoyancy The partially or fully submerged object experiences more pressure at the bottom that on top, this creates a resultant up thrust force called buoyancy. Why objects float An object will rise or float if it is less dense than the substance it is in or if it displaces an amount of the substance that it is floating in greater than it weights, steel ships have a lot of air in them and therefore weigh less than the equivalent amount of water that the ship displaces, so it floats this is because the up thrust from the pressure is greater than the down force of the weight. Atmospheric pressure and how it varies by altitude Air pressure is created by air molecules colliding with a surface, if we consider the density of these particles being same at all attitudes, the fact the volume of the earth's atmosphere increases as we rise in altitude then we can tell that the air pressure will decrease as there is more space for the same amount of particles to bump into each other. Also air is naturally less dense further away from the ground, reducing collisions and therefore pressure. Distance How far an object moved regardless of direction (scalar). Displacement The length of a straight line from the starting point to the finish point with its direction (vector). Walking speed estimate 1.5 m/s Running speed estimate 3 m/s Cycling speed estimate 6 m/s Car speed estimate 13-30 m/s Train speed estimate 50 m/s Aeroplane speed estimate 250 m/s Equation for distance Distance travelled = speed x time Velocity Velocity is a vector quantity representing speed in a certain direction. This means that a circular motion at a constant rate has a constant speed but a constantly changing velocity. Characteristics of a distance-time graph - a flat line means no movement, a change in time but not in distance. - a straight positive line represents a constant movement. - a concave curve represents an acceleration, a convex represents deceleration. - the speed at any point during an acceleration or deceleration can be determined by drawing a tangent Acceleration equation chance in velocity/time Velocity-Time graph characteristics -a flat line means no acceleration, a constant speed. - a straight positive line represents a constant acceleration, concave and exponential acceleration and convex a decreasing acceleration. - no movement is represented by a flat line on the x axis. - the area under the line equals the distance travelled. Terminal velocity explanation Near the Earth's surface any object free falling has an acceleration of 9.8m/s due to gravity. An object falling through a fluid will fall at 9.8m/s until the resultant force (from weight and resistance) is 0 and the object moves at its terminal velocity Process of reaching terminal velocity 1.Accelerates due to weight. 2.Air resistance increases with velocity, weight does not. 3.Air resistance becomes equal to weight, the forces become equal Newton's First Law If a resultant force acting on an object is zero, the object will remain stationary (this is inertia) or if it is moving, it will continue to move at the same velocity. Newton's Second Law The acceleration of an object is proportional to the resultant force acting on the object and inversely proportional to its mass. Resultant force equation Resultant force = mass x acceleration Inertial mass Inertial mass is a measure how difficult it is to change the velocity of an object. It is the ratio of force over acceleration (f=ma rearranged) Newton's Third Law Whenever two objects interact, the forces they exert on each other are equal and opposite. This is explains the result of equilibrium situations. How to find stopping distance stopping distance = thinking distance + braking distance Factors affecting reaction time - tired. - drunk. CONTINUED......