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Block 1 in the figure below has mass 1.00 kg, and block 2 has mass 3.00 kg . The

ID: 2006009 • Letter: B

Question

Block 1 in the figure below has mass 1.00 kg, and block 2 has mass 3.00 kg . The blocks are forced together, compressing a spring between them; then the system is released from rest on a level, frictionless surface. The spring, S, which has negligible mass, is not fastened to either block and drops to the surface after it has expanded. Block 2 acquires a speed of 1.20 m/s .
I have already found the velocity for block 1 : 3.6 m/s.

I am looking for the amount of potential energy stored in the compressed spring.

Explanation / Answer

As the total energy of the system is to be conserved, elastic potential energy of the spring = the total kinetic energy of the blocks potential energy of the spring = 0.5m1v12 + 0.5m2v22 potential energy of the spring = 0.5(1 kg)(3.6 m/s)2 + 0.5(3 kg)(1.2 m/s)2 potential energy of the spring = 8.64 J potential energy of the spring = 8.64 J