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I thought I knew how to solve for this problem but alas I was wrong. I'm hoping someone will be able to point me in the right direction.

Here's the problem: A 1.40x10^2 kg piano is being lifted at a steady speed from ground level straight up to an apartment 18.0m above the ground. The crane that is doing the lifting produces a steady power of 4.00x10^2 W. How much time does it take to lift the piano?

So here's what I did:

The equation for power is P = W/t.

The equation for W (work done) is W = (Fcos0)s.

I have P (at least this is my thinking here). P is 4.00x10^2 and I would need to find W and then I could solve for t.

F = ma, however I don't know what my acceleration is. I calculated it with 9.80 but my answer was incorrect. So if all my original thinking in finding t is correct then all I really need help with is finding F.

Any help provided will be greatly appreciated.