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Question
A spring is kept compressed by a small trolley of mass 0.5 kg lying on a smooth horizontal surface as shown in the adjacent fig. When the trolley is released, it is found to move at a speed v = 2 m s-1. What potential energy did the spring possess when compressed?
Solution
Mass of trolley = 0.5 kg
Velocity = 2 m/s
When the compressed spring is released, its potential energy is converted into kinetic energy completely.
Potential energy of compressed spring = kinetic energy of moving trolley
Kinetic energy of trolley = `1/2 × "mass" × ("velocity")^2`
= `1/2 × 0.5 × (2)^2`
= `1/2 × 0.5 × 2 × 2`
= 1J
Hence, potential energy of compressed spring = 1.0 J.
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