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# Physics problem about work and power....?

Show all steps please:

-List the givens

-List what unknown value you are finding

-Show the equations you're using and use all units.

-And please explain how you convert Newtons to mass in this problem.

Lisa runs up 4 flights of stairs in 22 seconds.

She weighs 510 Newtons.

If each flight rises 310 cm.....

1) What work does Lisa do?

2) What average power is required? (in 22 s)

3) If the human muscle is only 20% efficient, how many joules must Lisa take in from food in order to complete this task?

Here's what I've got:

t=22 s

d=310cm*4=1240cm=12.4m

m=510N=?

E= 20%= 0.20

And as far as equations go...

W=Fd (Work=Force*Distance)

P=W/t=Fd/t (Power=Work/time=(Force*Distance/time))

E=Wout/Win (Efficiency=Work output/ Work input)

Thanks for your time!

Trying to find: W=?, P=?, W=?.... again?

### 1 Answer

- Ossi GLv 79 years agoFavorite Answer
Hello

1) the work to do is

W = mgh = 510 N*(4*3.1 m) = 6324 J ( is = potential energy at a height of 4*3.1 m )

2) Power = work/time = 6324 Nm/22s = 287.45 Watt

3) The energy used is 6324 J. She must eat 5 times 6324 J = 31 620 J

Regards