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Spring Compression problem!

A 2.4kg block is dropped onto a free-standing spring with k=1100N/m from a height of 1.7m above the spring. What is the spring's maximum compression?

Okay, so I drew a picture of the situation.

Frame #1:

Falling Block: kinetic energy, but no potential energy

Spring: No kinetic energy and no potential energy

Frame #2:

Block has now compressed the spring to the maximum it is able.

Block and Spring: potential energy, but no kinetic energy

(If this reasoning is wrong so far, please let me know what is wrong about it and why! Thanks! :D)

So:

Energy in Frame #1 = Energy in Frame #

(Kf + Uf) = (Ki + Ui)

[0 + 1/2(k)(x^2)] = [1/2(m)(v^2) + 0]

([1/2(1100)(x^2)] = [1/2(2.4)(5.77)^2]

x = .2695m

I found the velocity for this equation by: (vf)^2 = (vi)^2 + 2ad

Vf= 5.77m.s

So that was how I found the max. compression of .2695m...

But in class, my teacher got the answer: .29m

He wrote the equation for this problem as: mgh + mgx = 0 + 1/2(k)(x)^2

How does he have 2 potential energies on the left side of the equation?! The block is moving! Wouldn't there be just a kinetic energy???

Please help me! Can the problem be done as I have done it, or is this wrong?

Please explain WHY it is wrong, if that is so.

Thank you SO much! :D You are awesome!!!

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# Homework Help: Spring Compression problem!- PLEASE SOMEONE HELP! PLEASE DX<?

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