A particle moves in the x – y plane under the influence of a force such that its linear momentum is p(t) =A[^icos(kt)−^jsin(kt)], where A and k are constants. The angle between the force and the momentum is
90∘
→p(t) =A[^icos(kt)−^jsin(kt)]⇒→F(t)=d→p(t)dt=Ak[−^isin(kt)−^jcos(kt)]
Now, finding the dot product, →p(t).→F(t)=0
Hence, angle is 90∘.