### Chapter #7Work , Power and Energy : Short Q/A / C.R.Q's

Q. If a cup it dropped and break into pieces then discuss the energy change.
Ans. There will be the following energy changes
* Potential energy of cup changes into kinetic energy
* The kinetic energy that converts into heat and sound energy.
* due to breaking the energy in the bonds of cup atoms breast and also converts into heat.

Q. A man standing still talking to his friend and the running engine of a stationary car. Write the similarity between two w.rt Work?
Ans. With respect to work Both are very much similar because A man standing still talking to his friend is not doing any work according to the physics and also the running engine of a stationary car is not doing work because the car is stationary.

Q.When a rocket re-enters the atmosphere, its nose become very hot .Where does this heat energy come from?
Ans. When the rocket comes back in to the atmosphere its nose become hot due to the work done against friction. As we know that the atmosphere is the upper sphere of gases on the earth. so the rocket having the potential energy changes some of its potential energy in the work done against friction that why nose becomes hot.

Q. Why we become physically tired when we push against a wall, fail to move it and therefore don’t work on the wall?
Ans. In this case although the wall does not changes its position so the work is zero but during the application of the force our muscles expand and contracts .This expansion and contraction of the muscles utilizes the energy so we become physically tired.