A particle of charge `= 1 muC` and mass m=1 gm starts moving from origin at t = 0 under an electric field of `10^(3) N//C` along x-axis and magnetic field of 10 tesla along the same axis with the velocity of `vec(v) = 20 hat(j)` m/sec as shown, the speed of the particle at the time of `20 sqrt(3)sec` will be :

Options

A. 20 m/sec
B. 40 m/sec
C. 10 m/sec
D. None

Answer

B

Explanation

As `V^(2)=V_(x)^(2)V_(y)^(2)=((qE)/(m)t)^(2)+(20)^(2)`
`=((10^(-6)10^(3))/(10^(-3))20 sqrt(3))^(2)+(20)^(2)=1600`
`V = 40 m//sec`