Question

A box on a rough floor is pushed with a force of 15 N, as shown in the figure, but it does not move. (a) What is the size and direction of the friction on the box? Name this friction. (b) The push is then increased to 25 N and the box starts sliding. The sliding friction is now 20 N. Find the net force on the box and its direction.

Two blocks A and B are held fully under water and then released. The figure shows the weight and the buoyant force on each block (arrows to scale). (a) Find the net force on each block just after release, with direction. (b) Which block will rise and float, and which will sink? Give reason.

Riya cycles 3 km to school every day. Her father oils the chain and the axles of her bicycle every Sunday. On a dry, sandy stretch of road she finds pedalling much harder than on the smooth tar road. When she presses the brakes, the brake rubber pads press against the wheel rims and the bicycle slows down.