A block of mass 15 kg is placed on a long trolley . The coefficient of friction between the block andthe trolley is 0.18. The trolley accelerates from rest with 0.5ms^(-2) for 20s and then moves with uniform velocity. Discuss the motion of theblock as viewed by (a) a stationary observer on theground (b) as observer moving with the trolley.

A block of mass 15 kg is placed on a long trolley . The coefficient of

1.	A block of mass 15 kg is placed on a long trolley . The coefficient of friction between the block andthe trolley is 0.18. The trolley accelerates from rest with 0.5ms^(-2) for 20s and then moves with uniform velocity. Discuss the motion of theblock as viewed by (a) a stationary observer on theground (b) as observer moving with the trolley.
Answer» Solution :`F_(s)=mu_(s)N=mu_(s)mg=0.18xx15xx9.8=26.46N`. Force on block `=F=ma=15xx7.5=7.5N F_(s) GT F`.So the block cannot move. (a) The stationary OBSERVER will see the accelerated and the uniformmotion . (b) The observeris in an accelerated FRAME. So laws of motion are not applicable. But during uniform motion, he will see that the block is at REST w.r.t him.