1.

A particle moves in X-Y plane under the action of forces F such that the values of linear momentum p at any times is px​=2cost and py​=2sint. The angle between F and p​ at the time t will be: (A) θ = 0°(B) θ = 30° (C) θ = 90°(D) θ = 180°​

Answer»

From Newtons second LAW, Force F is nothing but rate of change of momentum. Hence,  F = dP/dt Given, Px = 2cost  &  PY = 2sint => Fx = -2sint   &   Fy = 2cost Now to find the angle between the force vector and the momentum vector, let us first find the dot product of these two VECTORS. F.P = FxPx + FyPy       = 2cost*-2sint + 2sint*2cost       = -4cost*sint + 4cost*sint       =  0 ALSO, F.P = |F||P|cosθ =>  cosθ = 0 =>  θ = 90 degrees. Hence, the angle between force and momentum vectors is 90 degrees



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