1. The problem statement, all variables and given/known data Sand drops are falling gently at the rate of 2 kg/sec on a conveyor belt moving horizontally with a velocity of 5 m/s. Find the extra force and power required to keep the conveyor belt moving at constant speed. 2. Relevant equations Total work done on a body= Change in kinetic energy Force=dP/dt 3. The attempt at a solution For finding the extra force I use: Force=dP/dt Change in momentum of sand=2*5=10 Kg m/s per second therefore F=10 newton here the answer matches with the one given in my book. for power Power=WorkDone/Time Total work done on a body= Change in kinetic energy =0.5*2*5*5=25 J Therefore the answer =25 watt but the answer at the back of my book says 50 watt. I am confused. Where am I wrong?