# Q. The system shown in the figure is initially at rest and is being pulled by a force F= 18 N to the right. Given m=1 kg. Find the work done by friction as seen by observer stationary with respect...

Q. The system shown in the figure is initially at rest and is being pulled by a force F= 18 N to the right. Given m=1 kg.

Find the work done by friction as seen by observer stationary with respect to block of mass 3m

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### 1 Answer

The figure shows a block of mass 3 kg that is being pulled by a force 18 N to the right. The block is placed on a frictionless surface. On the block is a smaller block with mass 2 kg. This is connected by a string that passes around pulleys to a block with mass 1 kg placed on the frictionless surface that the 3 kg block is on. The coefficient of friction between the 3 kg block and the 2 kg bock placed on it is 0.5.

From the point of view of an observer stationary with respect to the block with mass 3m, there is a force of friction acting on the block of mass 2 m towards the left. To determine the work done by this force, the displacement has to be known as work is the product of force and displacement. As the displacement is not available here, the work done cannot be determined.