Exercise 7.2
Fill in the blanks. (i) Work done = ______ × ______ (in the direction of force). (ii) joule of work is done when a force of ______ newton displaces an object by metre in the direction of the force. (iii) The expression for kinetic energy of a body of mass m and velocity v is ______. (iv) The potential energy of an object of mass m at a small height h from the Earth’s surface is ______. (v) Power is defined as the ______ at which work is done.
NCERT’s answer
(i)
Force; Displacement $\displaystyle 1$ $\displaystyle 2$ $\displaystyle 2$ mv (ii) $\displaystyle 1$ (iii) (iv) mgh (v) rate
(i) Work done = force × displacement (in the direction of force).
(ii) A force of $\displaystyle 1$ newton — since \(\displaystyle 1\ \text{J} = 1\ \text{N} \times 1\ \text{m} \).
(iii) Kinetic energy \(\displaystyle = \) \(\displaystyle \frac{1}{2}mv^{2} \).
(iv) Potential energy \(\displaystyle = \) \(\displaystyle mgh \).
(v) Power is the rate at which work is done, \(\displaystyle P = \dfrac{W}{t} \).