1. Work

2. What is work?
“When an object is moved by a force we say that work is done on the object by a force” The force is transferring energy to the object. The amount of energy transferred is equal to the work done on it.

3. Energy transferred = work done
Calculating work done
Energy transferred = work done
Work done = force applied x distance moved in direction of force
W = F x d
W = work done in joules, J
F = force in newtons, N
d = distance moved in direction of the force, m

4. How much work?
A builder pushes a wheelbarrow a distance of 10.0m across flat ground. He uses a force of 100N so how much work does he do?
Work done = force applied x distance moved in direction of force
W = F x d
= x
= J
100 10
1000

5. How much work?
Eddie Hall pushed a 2 tonne truck just over 20 metres in 18 seconds.
How much work did he do?
W = F x d
= x
= J
20,000 20
400,000

6. Which one of these involves doing the most work?
Write down a definition for work
For each write down how you determined the work done and what the final value was
Lifting a (full) mug of tea from the desk to your mouth
Opening the classroom door
Pulling back your chair to sit down
Writing 10metres of English work
Climbing on the desk to close a window

7. Friction
Rub your hands together. What happens? Your muscles do work to overcome friction and this is transferred into heat energy Brake pads become hot if you apply the brakes for too long. Friction between the brake and the wheel slows down the vehicle. Most of the energy is transferred into heat (and maybe some sound)

8. gravitational potential kinetic sound
Q1.          (a) The weightlifter in the picture has lifted a weight of 2250 newtons above his head. The weight is held still.
(i)      In the box are the names of three forms of energy.
Which one of these forms of energy does the weight have?
(1)
(ii)     What force is used by the weightlifter to hold the weight still?
Size of force = N
Give a reason for your answer
(2)
(b)     To lift the weight, the weightlifter does 4500 joules of work in 3.0 seconds.
          Use the following equation to calculate the power developed by the weightlifter. Show clearly how you work out your answer.
Power = Watts (2) (Total 5 marks)
gravitational potential          kinetic          sound

9. M1.          (a)     (i)      gravitational potential
accept gravitational
accept potential 1
(ii)     2250 (N)
         forces must be balanced or forces are equal and opposite
do not accept because it is not moving do not accept ‘equilibrium’ by itself do not accept ‘it is not balanced’ do not accept ‘forces are equal’ do not accept ‘forces are the same’
(b)     1500
1 mark for correct substitution 2
[5]

10. E1.          This question was generally answered well although very few achieved the maximum 5 marks. The principal error was in part (a)(ii) where statements purely confirming the correct choice of 2250 N could not be credited. Candidates failed to state that if the weight is held still then the force used by the weightlifter must act in the opposite direction to the downward force of the weight.