Question

ANSWER WITH EXPLANATION... EQUATION FOR AVERAGE VELOCITY IN THIS CASE....WRONG ANSWERS FOR POINTS WILL NOT BE TOLERATED​

Answer 1

Let the total displacement of the body be $\sf{3x}$ so that each one - third of the distance measures $\sf{x.}$

Let the time taken by the body to cover first one - third of the distance be $\sf{t_1}$ given by,

$\longrightarrow\sf{t_1=\dfrac{x}{20}}$

Let the time taken by the body to cover second one - third of the distance be $\sf{t_2}$ given by,

$\longrightarrow\sf{t_2=\dfrac{x}{30}}$

Let the time taken by the body to cover last one - third of the distance be $\sf{t_3}$ given by,

$\longrightarrow\sf{t_3=\dfrac{x}{40}}$

Hence average velocity of the body is,

$\longrightarrow\sf{v_{av}=\dfrac{3x}{t_1+t_2+t_3}}$

$\longrightarrow\sf{v_{av}=\dfrac{3x}{\dfrac{x}{20}+\dfrac{x}{30}+\dfrac{x}{40}}}$

$\longrightarrow\sf{v_{av}=\dfrac{3x}{x\left(\dfrac{1}{20}+\dfrac{1}{30}+\dfrac{1}{40}\right)}}$

$\longrightarrow\sf{v_{av}=\dfrac{3}{\left(\dfrac{1}{20}+\dfrac{1}{30}+\dfrac{1}{40}\right)}}$

$\longrightarrow\sf{v_{av}=\dfrac{3\times20\times30\times40}{20\times30+30\times40+40\times20}}$

$\longrightarrow\sf{v_{av}=\dfrac{72000}{600+1200+800}}$

$\longrightarrow\sf{v_{av}=\dfrac{72000}{2600}}$

$\longrightarrow\underline{\underline{\sf{v_{av}\approx28\ m\,s^{-1}}}}$

Hence (1) is the answer.