# Homework Help: Box with spring coneected

1. Nov 26, 2007

### ~christina~

[SOLVED] box with spring coneected

1. The problem statement, all variables and given/known data

2 Blocks of mass M and 3M are placed on a horizontal frictionless surface. A light spring is attatched to one of them and the blocks are pushed together with the spring between them. A cord initally holding the blocks together is burned; after that happens, the block of mass 3m moves to the right with a speed of 2.00m/s

a) What is the velocity of the block of mass M?

b)find system's original elastic potential E, taking the M= 0.350kg

c) Is the original energy in the spring or cord?

d) Is the momentum of the system conserved in the bursting-apart process?
How can it be with no motion beforehand and plenty of motion afterward?

http://img208.imageshack.us/img208/6215/boxwithstringsb5.th.jpg [Broken]

2. Relevant equations

Ki= Kf

3. The attempt at a solution

$$SOLVED$$ (figured it out)

Last edited by a moderator: May 3, 2017
2. Nov 27, 2007

### rl.bhat

In this system the total energy is conserved. Therefore PE of the spring is equal to the total KE of M and 3M. Here spring constant or amount of compression is not needed. While calculating cancel M.

3. Nov 27, 2007

### ~christina~

Oh..I just figured that out while waiting for a response to my post.

Thanks