Question

A body has speed V,2V, and 3V in first 1/3 distance S, seconds 1/3 of S and third 1/3 of S respectively. Its average speed will be:

• A. V
• B. 2V
• C. $18/11V$
• D. $11/18V$

Answer 1

The correct option is C $18/11V$

Average speed $=\frac{TotalDistance}{TimeTaken}$

Time Taken in covering first $\frac{1}{3}$ distance of $o$

$t_1=\frac{S/3}{V}$

Time Taken in covering second $\frac{1}{3}$ distance of $s$

$t_2=\frac{S/3}{2V}$

Time Taken in covering Third $\frac{1}{3}$ distance of $s$

$t_3=\frac{S/3}{3V}$

Total time $=t_1+t_2+t_3=\frac{S/3}{V}+\frac{S/3}{2V}+\frac{S/3}{3V}=\frac{11S}{18V}$

$\therefore Averagevelocity=\frac{Totaldistance}{Totaltime}=\frac{S}{\frac{11S}{18V}}=\frac{18V}{11}$