Force exerted on a block

1. Feb 1, 2010

duckywucky

1. The problem statement, all variables and given/known data

During World War II, 16 huge wooden hangers were built for the U.S. Navy airships. The hangers were over 300 m long and had a maximum height of 52.0 m Imagine a 40.0 kg block being lifted by a winch from the ground to the top of the hanger's ceiling. If the winch does 2.08 x 10^4 J of work in lifting the block, what force is exerted on the block?

2. Relevant equations

KE = 1/2 mv^2
Net Work = deltaKE

3. The attempt at a solution

Could someone please explain to me, in detail, what to do here?
if you can, much appreciated!
Thank You

2. Feb 2, 2010

tiny-tim

welcome to PF!

well, hello duckywucky! welcome to pf!

(have a delta: ∆ and try using the X2 tag just above the Reply box )
No, ∆KE = 0 (it's not launching the thing, is it? )

Try ∆PE.

3. Feb 2, 2010

duckywucky

So does that mean I would do (40.0)(9.81)(2.08 x10^4)?
I came up with 814.192 but in scientific notation, it would be: 8.16 x 10^6 J?

4. Feb 2, 2010

tiny-tim

why?? explain in words.

5. Feb 2, 2010

duckywucky

I have no idea to be honest. Our class hasn't covered potential energy yet so i don't know what the formula is for it. XD

6. Feb 2, 2010

tiny-tim

hmm … thought so!

ok, so presumably the only equation you know is work done = force times distance.

in that case, what figures have you been given that you can put into that equation?

7. Feb 2, 2010

duckywucky

Work done is 2.08 x 10^4.
You're looking for Force, but i'm not sure the distance...maybe 300 m?

8. Feb 2, 2010

tiny-tim

"lifted by a winch from the ground to the top of the hanger's ceiling" …

that's not 300 m.

9. Feb 2, 2010

duckywucky

Work done is 2.08.
Force of gravity is 9.81
And the mass of the block is 40.0 kg.