NCERT Solutions for Chapter: Work and Energy, Exercise 5: Exercises

 An electric heater is rated $1500 \mathrm{W}$. How much energy does it use in $10$hours? 

Illustrate the law of conservation of energy by discussing the energy changes which occur when we draw a pendulum bob to one side and allow it to oscillate. Why does the bob eventually come to rest?  What happens to its energy eventually? Is it a violation of the law of conservation of energy? 

An object of mass, $m$ is moving with a constant velocity, $v$. How much work should be done on the object in order to bring the object to rest?  

Calculate the work required to be done to stop a car of $1500 \mathrm{kg}$ moving at a velocity of $60 \mathrm{km}/\mathrm{h}$? 

In each of the following a force, $F$ is acting on an object of mass, $m$. The direction of displacement is from west to east shown by the longer arrow. Observe the diagrams carefully and state whether the work done by the force is negative, positive or zero.

Soni says that the acceleration in an object could be zero even when several forces are acting on it. Do you agree with her? Why? 

Find the energy in $\mathrm{kWh}$ consumed in $10 \mathrm{hours}$ by four devices of power $500 \mathrm{W}$ each. 

A freely falling object eventually stops on reaching the ground. What happens to its kinetic energy?