A small block of mass 25 kg is on a long, horizontal table. Each side of the block is connected to a small sphere by means of a light inextensible string passing over a smooth pulley. Fig. 2 shows this situation. Sphere A has mass 5 kg and sphere B has mass 20 kg . Each of the spheres hangs freely.
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\caption{Fig. 2}
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Initially the block moves on a smooth part of the table. With the block at a point O , the system is released from rest with both strings taut.
- (A) Is mechanical energy conserved in the subsequent motion? Give a brief reason for your answer.
(B) Why is no work done by the block against the reaction of the table on it?
The block reaches a speed of \(1.5 \mathrm {~m} \mathrm {~s} ^ { - 1 }\) at point P . - Use an energy method to calculate the distance OP.
The block continues moving beyond P , at which point the table becomes rough. After travelling two metres beyond P , the block passes through point Q . The block does 180 J of work against resistances to its motion from P to Q .
- Use an energy method to calculate the speed of the block at Q .