A block of mass 100g slides on a rough horizontal surface. If the speed of the block decreases from 10 m s^–1 to 5 m s^–1, find the thermal energy developed in the process.

A brick weighing 4.0 kg is dropped into a 1.0 m deep river from a height of 2.0 m. Assuming that 80% of the gravitational potential energy is finally converted into thermal energy, find this thermal energy in calorie.

A van of mass 1500 kg travelling at a speed of 54 km h^–1 is stopped in 10 s. Assuming that all the mechanical energy lost appears as thermal energy in the brake mechanism, find the average rate of production of thermal energy in cal s^–1.

Two blocks of masses 10 kg and 20 kg moving at speeds of 10 m s^–1 and 20 m s^–1 respectively in opposite directions, approach each other and collide. If the collision is completely inelastic, find the thermal energy developed in the process.

A ball is dropped on a floor from a height of 2.0 m. After the collision it rises up to a height of 1.5 m. Assume that 40% of the mechanical energy lost goes as thermal energy into the ball. Calculate the rise in the temperature of the ball in the collision. Heat capacity of the ball is 800 J K^–1.