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$v. The kinetic energy of a body of mass 2 \mathrm{~kg} is 25 \mathrm{~J} . Its speed is(a) 5 \mathrm{~ms}^{-1} (b) 12.5 \mathrm{~ms}^{-1} (c) 25 \mathrm{~ms}^{-1} (d) 50 \mathrm{~ms}^{-1}$

$A car mass 800 \mathrm{~kg} traveling at 54 \mathrm{kmh}^{-1} is brought to rest in 60 meters. Find the average retarding force on the car. What has happened to original kinetic energy?$

$An object has 1 \mathrm{~J} of potential energy. Explain what does it mean?$

$When a rocket re-enters the atmosphere its nose cone becomes very hot. Where does this heat energy come from?$

$6.6 Define K.E. and derive its relation.$

$6.10 An electric motor of 1 \mathrm{hp} is used to run water pump. The water pump takes 10 minutes to fill an overhead tank. The tank has a capacity of 800 litres and height of 15 \mathrm{~m} . Find the actual work done by the electric motor to fill the tank. Also find the efficiency of the system.$

$What sort of energy is in the following:(b) Water in a high dam$