Physics (AS & A Level) · Feb / March 2021 · Paper 12 · Question 15

Two blocks, X and Y, are on a horizontal frictionless surface. The mass of block Y is greater than that of block X. Block Y has a spring attached to its end. The blocks are pushed together so that the spring is compressed between them and the blocks are held stationary as shown. [diagram: blocks X and Y on frictionless surface with compressed spring between them, before release] When released, the blocks move in opposite directions. Which statement is correct?

1. AAfter release, the kinetic energy of block X must equal the kinetic energy of block Y.
2. BAfter release, the sum of the kinetic energies of the blocks is equal to zero.
3. CThe total energy of the spring and blocks immediately before release is zero.
4. DThe total energy of the spring and blocks is equal to the energy needed to bring the blocks together.

As printed in the paper