11. A block of mass 2.0 kg is released from rest at point P as shown in the ﬁgure below. It is found that the block ﬁnally comes to rest at point Q.
The length of the track PQ is 2.5 m What us the average value of frictional force acting on the block when it is moving from P to Q?
All the initial energy of the block was lost to work done against friction.
The average frictional force is 4.0 N.