Question

A particle of positive charge q and mass m enters with velocity `Vhati` at the origin in a magnetic field `B(-hatk)` which is present in the whole space. The charge makes a perfectely inelastic collision with an identical particle (having same charge) ar rest but free to move at its maximum positive y-coordinate. After collision, the combined charge will move on trajectory where `r=(mV)/(qB)`.
A. `y=(mv)/(qB)x`
B. `(x+r)^2+(y-r//2)^2=r^2//4`
C. `(x+r)^2+(y-r//2)^2=r^2//8`
D. `(x-r)^2+(y+r//2)^2=r^2//4`

Answer 1

Correct Answer - b
Two particles will meet at P. After they meet they will stick together. Momentum mv will remain same. But charge is doubled, so radius is halved.

Finally, both move in dotted circle.