**Exercise-11.3 Page: 152**

**1. What is the kinetic energy of an object?**

**Solution:**

The energy possessed by a body by the virtue of its motion is termed mechanical energy or kinetic energy. Every moving object possesses mechanical energy. A body uses mechanical energy to try to work. Kinetic energy of the hammer is employed in driving a nail into a log of wood, mechanical energy of air is employed to run wind mills, etc.

**3. Write an expression for the kinetic energy of an object.**

**Solution:**

If a body of mass m is moving with a speed v, then its K.E. E k is given by the expression,

E_{k} = 1/2 m v^{2}

Its SI unit is Joule (J).

**4. The kinetic energy of an object of mass, m moving with a velocity of 5 ms**^{-1}** is 25 J. What will be its kinetic energy when its velocity is doubled? What will be its kinetic energy when its velocity is increased three times?**

**Solution:**