A 0.50-kg block attached to an ideal spring with a spring constant of 80 N/m oscillates on

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Question:

A 0.50-kg block attached to an ideal spring with a spring constant of 80 N/m oscillates on a horizontal frictionless surface. When the spring is 4.0 cm longer than its equilibrium length, the speed of the block is 0.50 m/s. What is the greatest speed of the block ?