Two particles of charges `+Q` and `-Q` are projected from the same point with a velocity v in a region of unifrom magnetic filed `B` such that the velocity vector makes an angle 'theta' with the magnetic filed Their masses are `M` and `2M` respectively Then, they will meet again for the first time at a point whose distane from the point of projection is .

Options

A. `2piM v cos theta//QB`
B. `8 piM v cos theta//QB`
C. `pi M v cos theta//QB`
D. `4 pi M v cos theta//QB`

Answer

D

Explanation

Both charge will move in helical path.
For +Q particle time period is `T=(2pim)/(QB)`. For -Q particle time period is `T=(4pim)/(QB)`
both will meet again after `t=(4pim)/(QB)`
Distance form point of porjection `=((4pim)/(QB))V cos theta=(4pi V cos theta)/(QB)`