Q. 64.5( 2 Votes )

# When a solid melts or a liquid boils, the temperature does not increase even when heat is supplied. Where does the energy go?

Answer :

When heat is supplied to melt solid or boil liquid, the heat energy is used in breaking the bond forces between the molecules of the solid or liquid to bring them apart until phase gets changed.

Hence the heat energy supplied to molecules is utilized as kinetic energy to overcome the molecular forces keeping the temperature constant.

This is what we call Latent Heat.

Rate this question :

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}.

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}.

Heat and work are equivalent. This means,

HC Verma - Concepts of Physics Part 2The temperature of a solid object is observed to be constant during a period. In this period.

HC Verma - Concepts of Physics Part 2A 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 copper cube of mass 200 g slides down on a rough inclined plane of inclination 37° at a constant speed. Assume that any loss in mechanical energy goes into the copper block as thermal energy. Find the increase in the temperature of the block as it slides down through 60 cm. Specific heat capacity of copper = 420 J kg^{–1} K^{–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.