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Question

A spring is compressed and stores 50 J of elastic potential energy. It is attached to a block resting on a frictionless horizontal surface. After the spring is released, what is the maximum kinetic energy gained by the block?

The correct answer is

50 J

On a frictionless surface no energy is lost to friction, so mechanical energy is conserved.

As the spring returns to its natural length, its elastic potential energy \(U = \frac{1}{2}kx^2\) is converted into kinetic energy of the block.

Maximum KE occurs when the spring reaches its natural length and all stored energy is transferred: \(K_{max} = U = 50\ \text{J}\).

Hence, the answer is 50 J.

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