Question

A block of mass m and charge q is connected to a point O with help of an extensible string. The system is on a horizontal table. An electric field is switched on in direction perpendicular to string. What will be tension when it become parallel to electric field?

• A. $\frac{qE}{2}$
• B. 3qE
• C. $\frac{qE}{l}$
• D. $\frac{3qE}{5}$

Answer 1

The correct option is B 3qE

$\Delta K.E=qEI=m{v}^2/2\Rightarrow m{v}^2/I=2qE$

Let, $T$ be the tension at final position

$T-qE=2qET=3qE$