Q. The 20 kg block shown in the figure is lying on a smooth horizontal plane is being pulled with a horizontal string that passes over a smooth,fixed pulley. A 5 kg block is kept on the 20 kg block and the coefficient of friction between the 5 kg block and the 20 kg block is 0.5.Find the acceleration of the 5 kg block. A) zero B) 2 `m/s^2` C) 2.5 `m/s^2` D) 5 `m/s^2`

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In the figure a 20 kg block is shown lying on a smooth horizontal plane, it is being pulled with a horizontal string that passes over a smooth, fixed pulley. A 5 kg block is kept on the 20 kg block and the coefficient of friction between the 5 kg block and the 20 kg block is 0.5. The coefficient of friction between the 20 kg block and the plane is 0.

When the 20 kg block is pulled with a force of 50 N, there is a force of friction between the 20 kg block and the 5 kg block. This is equal to `mu*N` = 0.5*5*10 = 24.5 N.

The acceleration of the 5 kg block is due to this force; the acceleration is 25/5 = 5 m/s^2.

The correct answer is option D

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