How Much Elastic Potential Energy Was Stored in the Spring Before Release?

[kevykevy]

Question-A child placed a spring of negligible mass between two toy cars of masses 0.112 kg and 0.154 kg. She compresses the spring and ties the cars together with a piece of string. When she cuts the string, the spring is released and the cars move in opposite directions. The 0.112 kg car has a speed of 1.38 m/s. What was the elastic potential energy stored in the spring before the string was cut?

Solution-I've tried to start this and I have no idea even where to begin. All I have so far is this picture I drew describing what's happening...

Spring Compressed
----

Spring Uncompressed (at rest)
- - - -

Before
Car1----Car2

After
Car1- - - -Car2

 

[OlderDan]

Question-A child placed a spring of negligible mass between two toy cars of masses 0.112 kg and 0.154 kg. She compresses the spring and ties the cars together with a piece of string. When she cuts the string, the spring is released and the cars move in opposite directions. The 0.112 kg car has a speed of 1.38 m/s. What was the elastic potential energy stored in the spring before the string was cut?

Solution-I've tried to start this and I have no idea even where to begin. All I have so far is this picture I drew describing what's happening...

Spring Compressed
----

Spring Uncompressed (at rest)
- - - -

Before
Car1----Car2

After
Car1- - - -Car2

What physical quantities do you think are conserved in this process?