JEE Main Physics question
A particle moves in the x-y plane under the action of a force F, such that its linear momentum p at a given time t is pₓ = 2cos t, = 2sin t. Then the angle θ between F and p at that time t is
Answer: (D)
Solution
F = dp/dt = (−2sin t, 2cos t). p·F = (2cos t)(−2sin t) + (2sin t)(2cos t) = 0, so F is always perpendicular to p; θ = 90°.