1. The problem statement, all variables and given/known data In the attachment! 2. Relevant equations P=F*v=F*d/t=Work/t KE=(mv^2)/2 W=f*s 3. The attempt at a solution For the first question, I Found it rather difficult to figure out WHAT exactly accelerated the sand. I would simply say the force of the engine? But at the same time in order for the sand falling to gain horizontal velocity it would need friction to keep it in place on the conveyor belt. But in what direction does the force of the friction act exactly? I feel like it'll just fall and plonk itself there. The force just holding it unto the conveyor belt! For the second question I'm more befuddled. To calculate this force I thought that perhaps I could use F= rate of change of momentum to solve it. So if initial velocity is 0 then the change will be 60*2=120. But then I find that perhaps one could use KE formula as well? I thought that if all the force goes into changing the velocity of the sand then i could backpedal (work=KE)/distance, but that yields 60N! half the amount! :S Calculating the power seems simple enough using the Power formula. But i'd either end up with 240 or 120, using the velocity 2 m/s and the 'KE-derived' force or the 'momentum' derived force. It later also asks why the rate of change of KE isn't the same as the power? I peeked at the answer after thinking long and hard and they wrote that it's due to loss of energy due to friction, gain in internal energy of conveyer belt. What confuses me with this is that I thought that the KE formula doesn't take this loss into account, or does it? I thought the KE formula would calculate the work change assuming that ALL the energy goes to change the object's KE, nothing else! To round off. I'm having trouble resolving the ideas of KE and F*d=W. I thought that the KE of the sand rate of change would be equal to F*2/time and also to the Power. Can anybody explain this to me in a concise manner? Thankyou so much. This site's a lifesaver.