Physics: Power

[shawonna23]

A 2.80*10^2 kg piano is being lifted at a steady speed from ground level straight up to an apartment 12.0 m above the ground. The crane that is doing the lifting produces a steady power of 4.00*10^2 W. How much time does it take to lift the piano?

i know that i have to use the equation Time= Work/Power. Power is given. How would I find work? i know that work=F*distance. Would work= 280*9.8*12.0=32928?

[shawonna23]

the answer i got 82.3 s. Is that correct?

[chroot]

Just make an energy argument.

How much potential energy does the piano gain by being hoisted up 12 meters? It's just PE = mgh, right?

The crane produces a specific amount of power. Power is work (or energy) per unit time.

Hoisting the piano requires x joules, and the crane can deliver P joules per second. The time it'll take is just x / P.

- Warren

[chroot]

Shawonna:

Looks good to me:

http://www.google.com/search?hl=en&q=2.8+*+10%5E2+kg+*+9.8+m%2Fs%5E2+*+12+m&btnG=Google+Search
http://www.google.com/search?hl=en&lr=&q=32928+joules+%2F+%284+*+10%5E2+joules%2Fsec%29&btnG=Search

- Warren