At a distance of 1 m from a fixed charge of 1 mC, a particle of mass 2 g and charge `1 muC` is held stationary. Both the charges are placed on a smooth horizontal surface. If the particle is made free to move, then its speed at a distance of 10 m from the fixed charge will be

Options

A. `100 ms^(-1)`
B. `90 ms^(-1)`
C. `60 ms^(-1)`
D. `45 ms^(-1)`

Answer

B

Explanation

Loss in EPE = gain in KE
`K_s+V_s=K_c+V_c, 1/2 mu^2 +q.q/(4 pi e_0 R)=0+q. (3q)/(8 pi e_0R), 1/2 mu^2=1/8. q^2/( pi e_0R)`
`u^2=q^2/(4 pi e_0 mR) implies u= q/ sqrt(4 pi e_0 mR)`