Work Done by a Spring Force

[AtlBraves]

I am having trouble with this part of the problem. I set it up like this: -.5*m*v^2 = -.5*k*d^2 so v = sqrt((k*d^2)/m) = sqrt((220*.14^2)/.25) = 4.15 m/s. What am I doing wrong?

A 250 g block is dropped onto a relaxed vertical spring that has a spring constant of k = 2.2 N/cm (Figure 7-42). The block becomes attached to the spring and compresses the spring 14 cm before momentarily stopping.

(c) What is the speed of the block just before it hits the spring? (Assume that friction is negligible.)

http://www.webassign.net/hrw/07_41.gif

[arildno]

Possibly, you should take into account the change in gravitational potential energy as well.

[AtlBraves]

I don't understand.

[daveed]

while the spring is compressing, gravity is still adding kinetic energy, even as the spring is taking it away. so you should see how much gravitational potential energy has been included after the 14 cm compression, and take that into account with your equation