A force of 100 N presses a 3 kg block against a vertical wall as shown. The coefficient of friction is 1/4. Find the frictional force acting on the block.

Question

G1 Physics · Accepted Answer

The 100 N force has an upward component 100 sin30° = 50 N, while the weight is 30 N downward. Without friction the block tends upward by 20 N, so friction acts downward with magnitude 20 N. The available limiting friction is sufficient.