A ball of mass 1g and charge `10^(-8) C` moves from a point A whose potential is 600V to the point B whose potential is zero. Velcoity of the ball at the point B is `20 cm s^(-1)`. The velocity of the ball at the point is

Options

A. `2.8 ms^(-1)`
B. `2.8 cm s^(-1)`
C. `16.7 m s^(-2)`
D. `16.7 cm s^(-1)`

Answer

D

Explanation

Gain in K.E. as it moves from point A to point B `600 V xx 10^(-8) C= 6 xx 10^(-6)J`
K.E. of the ball at `B= (1)/(2) mv^(2)`
`=(1)/(2) xx 10^(-3) xx (0.2)^(2) = 2 xx 10(-5)J`
`:. " K.E at" A= 2 xx 10^(-5) J-6 xx 10^(-6)J`
`= 14 xx 10^(-6)J`
`:.` Velocity at `A = sqrt((14 xx 10^(-6) xx 2)/(10^(-3))) = sqrt(28 xx 10^(-3)) m//s`
`=16.73 cm s^(-1)`