In a region of space, a uniform magnetic field `B` exists in the y-direction `A` proton is fired from the origin, with its initial velocity v making a small angle alpha with the y-direction in the yz plane. In the subsequent motion of the proton
.

Options

A. Its x coordinate can never be positive
B. Its x and z coordinates cannot both be zero at the same time
C. Its z coordinate can never be negative
D. Its y coordinate will be proportional to the square of its time of flight

Answer

A

Explanation

Path will be helix with axis `x=-R=-(mv sin alpha)/(qB)`