JEE Main Physics question
A particle moves in the X-Y plane under the influence of a force such that its linear momentum is **p**(t) = A[î cos(kt) − ĵ sin(kt)], where A and k are constants. The angle between the force and the momentum is
Answer: (D)
Solution
F = dp/dt = Ak[−î sin(kt) − ĵ cos(kt)]. p·F = A²k[−cos(kt)sin(kt) + sin(kt)cos(kt)] = 0 ⟹ θ = 90°.