In a certain region uniform electric field E and magnetic field B are present in mutually opposite directions. At the instant `t=0`, a particle of mass m carrying a charge q is given velocity `v_(0)` at angle `theta`, with the `y-` axis, in the yz plane. The time after which the speed of the particle would be minimum is equal to

Options

A. `(mv_(0))/(qE)`
B. `(mv_(0)sin theta)/(qE)`
C. `(mv_(0)cos theta)/(qE)`
D. `(2pim)/(qB)`

Answer

B

Explanation

`(b)` `v=u+at`
`O=v.sin theta-(qE)/(m)t,t=(mv_(0)sin theta)/(qE)`
Electric force will declerate the component `v_(0) sin theta` and will not effect to `v_(0)cos theta`