AP EAMCET Engineering 21 Apr 2019 Shift 1 Paper

A proton and an α-particle are simultaneously projected in opposite directions into a region of uniform magnetic field of 2 mT perpendicular to the direction of the field. After some time it is found that the velocity of proton has changed in direction by 90°. Then at this tune, the angle between the velocity vectors of proton and a-particle is