# Homework Help: Mass on Spring

1. May 25, 2010

### bon

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

Two identical masses m1 = m2 = m are connected by a massless spring with
spring constant k. Mass m1 is attached to a support by another massless spring with
spring constant 2k. The masses and springs lie along the horizontal x-axis on a smooth
surface. The masses and the support are allowed to move along the x-axis only. The
displacement of the support in the x-direction at time t is given by f (t) and is externally
controlled. Write down a system of diļ¬erential equations describing the evolution of the
displacements x1 and x2 of the masses from their equilibrium positions.

2. Relevant equations

3. The attempt at a solution

Is it: mx1'' = -k[x1-f(t)] + k[x2-x1-f(t)]

mx2" = -k[x2-x1-f(t)]

?

Thanks!

2. May 25, 2010

### ehild

Check your equations. The force exerted by a spring depends on the change of its length. Does an other spring effect this force?
Read the problem, are the spring constants equal?

ehild