Question

A 4 kg mass and a 9 kg mass are being held at rest against a compressed spring on a frictionless surface. When the masses are released, the 4 kg mass moves to the east with a speed of 2m/s. What is the velocity of the 9 kg after the are released?

Answer 1

This is a inelastic equation, so we use (m1+m2)vf = m1v1+m2v2, where m1 is 4 kg, m2= 9kg. The start with no velocity so Vf=0, meaning the left side is 0.
m1v1=4 times 2 =8, We subtract to the left side and divide by m2, 9kg. v2 = 8/9 heading west.