Pathfinder Methods of Work and Energy MCQ 14

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Q.14

One end of an elastic cord is attached to a block of mass m and the other end is held keeping the cord relaxed and vertical. Relaxed length of the cord is l and there is a mark P at a height 0.8l from the lower end. If the upper end is slowly raised, the block leaves the ground, when the mark P reaches the point where the upper end of the relaxed cord initially was. Expression for the work done by the force applied by the hand is