The Student Room Group

Spring Pick-up

A light spring with spring constant k is attached at one end to a block which moves with a constant velocity u

. At a time t=0s a hook at the other end of the spring attaches to a mass m.

If an external force is applied to the moving block so that it remains moving at a velocity of u

, what is the maximum speed obtained by the mass m?
The answer is 3.00 ms^-1. From hint 4, use the reference frame of the block. Initially, the spring has no extension and the mass is moving away from the block at 1.5 ms^1. The mass oscillates and moves back towards the block with speed 1.5 ms^1 in the opposite direction. Using the original reference frame, the velocity must be 1.5 + 1.5 = 3 ms^1

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