We can calculate power using this equation: $P=\frac{W}{t}$.

Copy and complete the table to show the units of each quantity in the equation.

Quantity	Unit
$P$
$W$
$t$

Millie and Lily are identical twins who enjoy swimming. Their arms and legs provide the force needed to move them through the water. Millie can swim $25 \mathrm{m}$ in $50 \mathrm{s}$. Lily can swim $100 \mathrm{m}$ in $250 \mathrm{s}$.

Calculate the swimming speed of each twin.

Millie and Lily are identical twins who enjoy swimming. Their arms and legs provide the force needed to move them through the water. Millie can swim $25 \mathrm{m}$ in $50 \mathrm{s}$. Lily can swim $100 \mathrm{m}$ in $250 \mathrm{s}$.

Which twin has the greater power when swimming? Explain how you can tell.

Jim is pulling a load along a ramp, as shown. The diagram shows the force with which he pulls and the weight of the load.

Calculate the work done by Jim's pulling force.

Jim is pulling a load along a ramp, as shown. The diagram shows the force with which he pulls and the weight of the load.

What is the gain in potential energy of the load?

Two girls are estimating each other's power. One runs up some steps, and the other times her. Here are their results:

Height of one step$=20 \mathrm{cm}$

Number of steps$=36$

Mass of runner$=45 \mathrm{kg}$

Time taken$=4.2 \mathrm{s}$

Calculate the runner's weight. (Acceleration due to gravity $g=10 \mathrm{m} {\mathrm{s}}^{-2}$.)

Two girls are estimating each other's power. One runs up some steps, and the other times her. Here are their results:

Height of one step$=20 \mathrm{cm}$

Number of steps$=36$

Mass of runner$=45 \mathrm{kg}$

Time taken$=4.2 \mathrm{s}$

Calculate the increase in the girl's gravitational potential energy as she runs up the steps.

Two girls are estimating each other's power. One runs up some steps, and the other times her. Here are their results:

Height of one step$=20 \mathrm{cm}$

Number of steps$=36$

Mass of runner$=45 \mathrm{kg}$

Time taken$=4.2 \mathrm{s}$

Calculate her power. Give your answer in kilowatts $\left(\mathrm{kW}\right)$.