Work, Energy and Power
• Work is the product of force and distance travelled in the direction of force.
Denoted by W. So here the work done is F*b.
Si unit is in joules.
Here the force applied needs to be constant and hence workdone will be equal to F cos
angle x *d. See the lines of how we resolved the vectors. Donot write it as F*cos x*d as
cos has to be only with the angle x so you can write it as F*d*cos x. If x is 0 degrees so
cos 0=1 hence formula is produced F*d and at this angle the force is doing the
maximum work. If force is upwards and distance is travelled upwards then use sin.
• When we take the cos of 180 the workdone becomes negative and this negative
sign shows the loss in energy. Workdone remember is the conversion of energy. It
is taken as positive when workdone on the system and indicates the gain in
energy while taken as negative when work is done by the system and appear as
the loss of energy.
figure 1
, • here the object travels the distance of 10 m and there is a friction force of 10 N
while the total workdone is going to be 100*10 =1000 and workdone by the
friction is 10*10 =100 so the net workdone is 900J. Remember that the total
workdone is the useful energy and the workdone by the friction is that negative
workdone indicating the loss in the energy. And this net workdone is the gain in
the energy.
Workdone by a Gas:
• a gas is enclosed in a cylinder while the volume is V1 and piston has area A. And
pressure downwards is p which is the atmospheric pressure.
• Heat is provided and the gas expands and the piston moves up and cover the
distance d. And now has the volume V2 while the atm pressure is still there.
• W=F.d
While F= p.A
So W=p.A.d and the A.d is the volume that will be the volume increase V2-V1.
Final equation is W= p* change in volume.
• If we are to find the workdone against the atmospheric pressure in thermal
expansion so we will multiply the atmospheric pressure value into the change
in volume that would obviously the increase in volume as the object is
expanding.
• Work is the product of force and distance travelled in the direction of force.
Denoted by W. So here the work done is F*b.
Si unit is in joules.
Here the force applied needs to be constant and hence workdone will be equal to F cos
angle x *d. See the lines of how we resolved the vectors. Donot write it as F*cos x*d as
cos has to be only with the angle x so you can write it as F*d*cos x. If x is 0 degrees so
cos 0=1 hence formula is produced F*d and at this angle the force is doing the
maximum work. If force is upwards and distance is travelled upwards then use sin.
• When we take the cos of 180 the workdone becomes negative and this negative
sign shows the loss in energy. Workdone remember is the conversion of energy. It
is taken as positive when workdone on the system and indicates the gain in
energy while taken as negative when work is done by the system and appear as
the loss of energy.
figure 1
, • here the object travels the distance of 10 m and there is a friction force of 10 N
while the total workdone is going to be 100*10 =1000 and workdone by the
friction is 10*10 =100 so the net workdone is 900J. Remember that the total
workdone is the useful energy and the workdone by the friction is that negative
workdone indicating the loss in the energy. And this net workdone is the gain in
the energy.
Workdone by a Gas:
• a gas is enclosed in a cylinder while the volume is V1 and piston has area A. And
pressure downwards is p which is the atmospheric pressure.
• Heat is provided and the gas expands and the piston moves up and cover the
distance d. And now has the volume V2 while the atm pressure is still there.
• W=F.d
While F= p.A
So W=p.A.d and the A.d is the volume that will be the volume increase V2-V1.
Final equation is W= p* change in volume.
• If we are to find the workdone against the atmospheric pressure in thermal
expansion so we will multiply the atmospheric pressure value into the change
in volume that would obviously the increase in volume as the object is
expanding.
