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Motion In A Plane

Question
CBSEENPH11020863

The x and y coordinates of a particle moving in a plane are given be x(t) = acos(pt) and y(t) = bsin(pt) where a, b (<a) and p are positive constants of appropriate dimensions and t is time. Then , which of the following is not true?

  • The path of the particle is an ellipse

  • Velocity and acceleration of the particle are perpendicular to each other at t = π/2p

  • Acceleration of the particle is always directed towards a fixed point

  • Distance travelled by the particle in the time interval between t = 0 and t = π/2p is a

Solution

D.

Distance travelled by the particle in the time interval between t = 0 and t = π/2p is a

x = a cos (pt), y =b sin (pt)

 x2a2 + y2b2 = 1, i.e. equation of ellipseNow, r = xi^ + yj^  = a cos (pt) i^  + b sin (pt)j^v = drdt = -pasin (pt) i^ + pb cos (pt) j^a = dvdt = - p2a cos (pt) i^ - p2 b sin (pt)j^at t = π2pv = - pa  i^   and a = - p2b j^ v  a 

also, a = - p2r, i.e directed towards a fixed point.