Work Done Flashcards

All 6 cards in this deck

When is work done on an object?

When a force causes the object to move through a distance (a displacement) along the line of action of the force.

What is the equation linking work done ($W$), force ($F$) and distance ($s$)?

work done = force $\times$ distance, or $W = F\,s$ (distance moved along the line of action of the force)

In $W = F\,s$, what unit is each quantity measured in?

$W$ in joules (J), $F$ in newtons (N), $s$ in metres (m).

True or false? If a force acts on an object but the object does not move, no work is done on the object.

True. Work needs a displacement: with $s = 0$, $W = F \times 0 = 0$ J.

What are the steps to calculate work done from a force and a distance?

e.g. a car travels 7.5 km against an air resistance of 4000 N

1. Convert the distance to metres: $7.5\text{ km} = 7500$ m
2. Substitute into $W = F\,s$: $W = 4000 \times 7500$
3. Work out the answer in joules: $W = 30\,000\,000$ J

What are the steps to find the force when you know the work done and the distance?

e.g. 35 J of work is done pushing a walker 2.8 m

1. Write the equation: $W = F\,s$, so $35 = F \times 2.8$
2. Rearrange: $F = \dfrac{W}{s} = \dfrac{35}{2.8}$
3. Answer in newtons: $F = 12.5$ N