Spring and Gravity Potential Energies

1. Nov 12, 2007

brendan3eb

1. The problem statement, all variables and given/known data
A 2-kg block is dropped from a height of 0.4 m onto a spring force whose constant k is 1960 N/m. Find the maximum distance the spring will be compressed.

2. Relevant equations
U1+K1=U2+K2

3. The attempt at a solution
both the initial and final kinetic energy should be 0 so we should get an equation like this:
mgh=(1/2)kx^2+mg(value)

I can't find an expression to put in for value that only has x and no other unknown variables.

2. Nov 12, 2007

G01

The expression you have will work.

Hint: Let the lowest point the block reaches be h=0m.

3. Nov 12, 2007

brendan3eb

so I would substitute 0 in for value to get x = .089 m, correct? Yeah, that's what I have been getting. However, my teacher told me the answer is 1.00 m. I am starting to wonder if he read off the wrong answer. Do you get .089 m too?

4. Nov 12, 2007

G01

I also get .089m. Check to make sure your numbers and units are correct. If they are, then I suggest talking to your teacher about it. Even teachers aren't perfect!

Technically, the method we are using assumed the spring is compressed a negligible amount, but I think this is a reasonable assumption that wouldn't change the answer that much.

Last edited: Nov 12, 2007