A 1 kg block lies on a 2 kg plank. The coefficient of friction between block and plank is 0.4, while that between plank and floor is 0.1. A horizontal force F = 10 N acts on the upper block. Find the acceleration of the plank.

Question

G1 Physics · Accepted Answer

If they moved together, the required friction on the 1 kg block would exceed μmg = 4 N, so the upper block slips. Friction on the plank is 4 N to the right. Floor friction is 0.1×(3×10)=3 N to the left. Net force on the 2 kg plank is 1 N, so a = 1/2 = 0.5 m s⁻².