Conservation of energy answers

Conservation of Energy

(Use g = 9.8 N kg^-1)

1. A waterfall is 120 m high. If 75 % of the potential energy available is converted into heat energy, find the difference in temperature between the top and bottom of the fall. The specific heat capacity of water is 4200 J kg^-1 K^-1.                                       .21K

2. A lead bullet moving at 210 m s^-1 is brought to rest on hitting a target. If 60 % of its energy is converted into heat energy, find the rise in temperature of the bullet. The specific heat capacity of lead is

140 J kg^-1 K^-1.                                   94.5K

3. A lump of lead falls to the ground and its temperature rises by 1.4 °C. If all the potential energy is converted into heat energy, find the height fallen, if the specific heat capacity of lead is 140 J kg^-1 K^-1.                20m

4. If 60 % of the potential energy available in a waterfall is converted into heat energy, find the height of the waterfall when the temperature difference between the top and the bottom of the fall is 0.21 °C. (The specific heat capacity of water = 4200 J kg^-1 K^-1.)                  150m

5. A paddle wheel is made to rotate inside a calorimeter containing water by a mass of 12 kg falling through a height of 2 m. The total heat capacity of the calorimeter and its contents is 800 J K^-1. Find the rise in temperature of the water.                        .294K

6. A car of mass 800 kg is moving at 108 km h^-1. What heat energy is produced in the brake drums when it is brought to rest by the brakes?             360 kJ

7. On entering the earth's atmosphere the velocity of a meteorite of mass 6 kg is reduced rapidly from 300 m s^-1 to 100 m s^-1. How much heat energy is produced?                  240 kJ

8. A lead bullet moving at 70 m s^-1 is brought to rest on hitting a target. If 80% of its energy is converted into heat energy, find the rise in temperature. (The specific heat capacity of lead = 140 J kg^-1 K^-1.)                  14K

9. A lead bullet at 40.5 °C before impact just melts when it hits a target without rebounding. If all the energy of the bullet is converted into heat energy, find the velocity of the bullet. (The specific heat capacity of lead = 140 J kg^-1 K^-1. The melting point of lead = 328 °C. The specific latent heat of fusion of lead = 21 000 J kg^-1.)                  350ms^-1