Question

While skiing in Jackson, Wyoming, your

friend Ben (of mass 56.1 kg) started his descent
down the bunny run, 16 m above the
bottom of the run.

12 s.
What is the average power expended by the
student to overcome gravity?
Answer in units of W.

Answer 1

Hello!

Work is equal to negative change in PE and PE=mgh and Power is change in work/change in time

So we have

56.1kg * 9.80m/s^2 * 16m = 8796.5 J of PE at top of run and -8796.5J of work done also

if it takes him 12s then we need to find the time gravity alone would bring him to the bottom. we get

16m=1/2at^2 and solving for t we get
t=sqrt(32/9.80m/s^2)=1.81s

so the difference in time is 12-1.8=11.2s

now we can find avg power=work/time = 8796.5J/11.2s = 785W or 785J/s

Hope this helps! Any questions please ask! Thank you!