Physics
posted by Carden .
A 0.409 kg block is attached to a horizontal spring that is at its equilibrium length, and whose force constant is 19.5 N/m. The block rests on a frictionless surface. A 0.0500 kg wad of putty is thrown horizontally at the block, hitting it with an initial speed of 2.32 m/s and sticking. How far does the puttyblock system compress the spring?
My answer .366 is 10% off. Why/How?

How can I possibly know why your answer is off? I have no idea what you did.

I did m1v1 /(m1+m2) = vf = .252723
x = vf(m/k)
x = .366 
after getting vf, you need to calculate the KE of the putty/block, and set that equal to the compressed energy in the spring 1/2 k x^2, and solve for x.
I think you need a tutor, you appear to be totally lost. 
x = v * sqrt(m/k)
correct? 
No.
Set the KE of the putty/block, set it equal to the max stored energy of the spring, 1/2 k x^2 
when I set 1/2mv2 equal to 1/2kx2
I got .366 
make sure you are converting your final answer to meters