Figure 10 shows a girl doing an experiment to determine her power output by running to the top of some stairs.
i- The mass of the girl was 60.0 kg.
The height of the stairs was 175 cm.
The girl ran to the top of the stairs in 1.40 s.
gravitational field strength = 9.8 N/kg
Calculate the power output of the girl.
Use the Physics Equations Sheet.
[5 marks]
SOLUTION
We know that power is energy per unit time. To know how much energy does the girl took to ran up the stairs, we need to know the GPE which is maximum at the height.
Now, applying the power formula.
ii- The total power output of the girl was greater than the answer to question i.
Suggest two reasons why.
[2 marks]
SOLUTION
This could be because
Girl increased her kinetic energy which in return would have increased the GPE.
Some energy must have been wasted as heat to surroundings.
iii- A boy took more than 1.40 s to run up the same stairs.
The power output of the boy was the same as the power output of the girl.
What conclusion can be made about the boy’s mass?
[1 mark]
SOLUTION
Since boy took more than 1.40 seconds, the mass of boy would be greater than girl’s, provided that the power putput, total height of the stairs and gravitational field are constant/same.
