Question

A $2$ - gram object, located in a region of uniform electric field $\overrightarrow{ E }=\left(300\, N C ^{-1}\right) \hat{ i }$ carries a charge $Q .$ The object released from rest at $x=0$, has a kinetic energy of $0.12\, J$ at $x =0.5$ $m$. Then $Q$ is

• A. $400\, \mu c$
• B. $-400\, \mu c$
• C. $800\, \mu c$
• D. $-800\, \mu c$

Answer 1

Answer: (C)

Work done $( W )=$ Change in $K E$
Force $\times$ displacement $=$ change in $KE$
$QE \times x =0.12\, J$
$ Q (300) \times(0.5)=0.12 $
$ Q =\frac{0.12}{300 \times 0.5}=800\, \mu C$
The charge $Q$ is moving in the direction of electric field, hence it is positive.