A proton with the rest mass of 1.67 × 10¬" kg is initially moving at 0.90c in the +x-direction,relative to the reference frame of a physics laboratory. Then a constant

force F = (-3.0 × 10-12 N)Î+ (5.0 × 10-12 N)ĵ is applied to the proton. What is the angle between the applied force and the resulting acceleration of the proton?