A 50 kg man pulls on a 100 kg plank on a smooth floor using the shown rope-pulley arrangement with a force of 100 N. If man and plank move together, find the friction force on the man.

Question

G1 Physics · Accepted Answer

The rope pulls both the man and the plank with 100 N, so total external horizontal force on the 150 kg system is 200 N and common acceleration is 4/3 m s⁻². For the man, 100 + f = 50(4/3), giving f = -100/3 N. Thus friction is 100/3 N to the left.