# Block and Springs

1. Oct 7, 2008

### Awwnutz

http://img232.imageshack.us/img232/9219/blockandspringsup8.gif [Broken]

A block of mass M = 1.5 kg slides between two springs, of spring constant kleft = 30 N/m and kright = 57 N/m. The distance between the relaxed springs is d = 2.8 m. The left spring is initially compressed a maximum of dleft = 0.7 m, and the block is released from rest. The first time the block hits the right spring, it compresses it a distance dright = 0.4 m Find the coefficient of sliding friction between the block and the surface.

Relevant equations:
Spring force: (1/2)mv^2
Work Energy Theorem: Change in Kinetic Energy = Work done on block

I haven't gotten too far on this one. I know i probably need to find the force of the spring on the left and how fast the block moves. Then use that velocity and the work done by the other spring to find the friction. Or something along those lines? Is this close? (Probably not)

Last edited by a moderator: May 3, 2017
2. Oct 7, 2008

### Awwnutz

I figured it out...

I had to do:
work done by friction = Change in potential energy

3. Jun 3, 2010

I have the same exact problem but I can't figure it out.

I used the equation (( W = 1/2 * kx^2 )) for both springs to get a net force of Wleft - Wright = 2.97 Nm.

In my understanding, this change in W caused by the work done by friction over the 2.8 m interval, so i solved W = F*d to get F = 0.9964 N.
((2.97 = F * 2.8))

0.9964 would be the force of friction, so i used the equations F = M*N and N = mg to solve for the friction constant (M).

The answer I came up with was 0.0667, but this is not right.