Question

A toy car with charge $q$ moves on a frictionless horizontal plane surface under the influence of a uniform electric field $\overrightarrow{E}$. Due to the force $q$$\overrightarrow{E}$, its velocity increases from $0m/s$ to $6m/s$ in one second. At that instant the direction of the field is reversed. The car continues to move for two more seconds under the influence of this field. The average velocity and the average speed of the toy car between $0$ to $3$ seconds are respectively

• A. $2m/s,4m/s$
• B. $1m/s,3m/s$
• C. $1m/s,3.5m/s$
• D. $1.5m/s,3m/s$

Answer 1

The correct option is B $1m/s,3m/s$

$0s<t<1s$ : velocity increases from $0m/s$ to $6m/s$
$1s<t<2s$ : velocity decreases from $6m/s$ to $0m/s$ but car continues to move forward
$2s<t<3s$ : Since field strength is same $\Rightarrow$same acceleration $\therefore$ car's velocity increases from $0m/s$ to $-6m/s$


Distance travelled in first second
$S=\left(\frac{u+v}{2}\right)t=\left(\frac{0+6}{2}\right)1=3mDistance=9m,soaveragespeed=\frac{9m}{3s}=3m/sDisplacement=3m,soaveragevelocity=\frac{3m}{3s}=1m/s$