A bullet of mass 20g enters into a fixed wooden block with a speed of 40 m s^–1 and stops in it. Find the change in internal energy during the process.

Calculate the time required to heat 20 kg of water from 10°C to 35°C using an immersion heater rated 1000 W. Assume that 80% of the power input is used to heat the water. Specific heat capacity of water = 4200 J kg^–1 K^–1.

On a winter day the temperature of the tap water is 20°C whereas the room temperature is 5°C. Water is stored in a tank of capacity 0.5 m³ for household use. If it were possible to use the heat liberated by the water to lift a 10 kg mass vertically, how high can it be lifted as the water comes to the room temperature? Take g = 10 m s^–2.

A 50 kg man is running at a speed of 18 km h^–1. If all the kinetic energy of the man can be 9used to increase the temperature of water from 20°C to 30°C, how much water can be heated with this energy?

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.