Question

A 15 kg object and a 18 kg object are connected by a massless compressed spring and

rest on a frictionless table. After the spring is
released, the object with the smaller mass has
a velocity of 12 m/s to the left.
What is the velocity of the object with the
larger mass?
Answer in units of m/s.

Answer 1

Hi there!

This is an example of a recoil collision.

Using the conservation of momentum:

`p_i = p_f`

The initial momentum is 0 kgm/s (objects start from rest), so:

`p_f = 0`

We are given that the 15 kg block has a velocity of 12 m/s to the left, so:

`m_1v_1' + m_2v_2' = 0 \\\\15(-12) + 18v_2' = 0 \\\\`

Solve for v2':

`18v_2' = 180 \\\\v_2' = \boxed{10 m/s}`