Work Done

Question 1

What is work done? (2)

Answer 1

-When work is done, energy is transferred.
- This causes a change in the energy store

Question 2

Which 3 processes transfer energy?

Answer 2

1. Heating
2. Radiation (light and sound)
3. An electrical current

Question 3

Can forces do work?

Answer 3

Yes (mechanically)

Question 4

Give an example of forces doing work

Answer 4

• When a bag is lifted, work is done against gravity
• When the bag is released, work is done by gravity

Question 5

What other force does work and what against?

Answer 5

Friction does work against moving objects

Question 6

State the equation for work done

Answer 6

Work done = force applied x distance moved in direction of force
W = F x s
(Joules) (Newtons) (metres)

Question 7

A 15kg goat is moved from the ground floor to the first floor in a lift. The first floor is 2.5m above the ground floor.
What is the work done?
(Hint: you will need two equations to answer this question)

Answer 7

E W=mg
U ✔️
S W=15 × 9.8
A ✔️
C 147N

E W= F x s
U ✔️
S W= 147 x 2.5
A ✔️
C 367.5 J= 370J to 2 s.f.

Question 8

Define 1 Joule

Answer 8

1 Joule of energy is transferred when a force of 1N acts on an object for a distance of 1m in the direction of the force.

Question 9

A brick is lifted 2.5m onto a wooden platform.
a. If the mass of the brick is 0.5kg, determine the work done on the brick.
b. How much does the store in GPE increase by?

Answer 9

a. The force used to lift the brick must be equal to the weight of the brick. Therefore:
Weight = mg = 0.5 × 9.8
Now we can determine the work done:
Work done = Fs = 4.9 × 2.5
= 12.25J
b. The work done on the mass = gain in GPE. Therefore, the brick gains Joules of GPE.