A particle moves so that its position vector is given by r → = c o s ω t x ^ + s i n ω t y ^ , where ω is a…

A particle moves so that its position vector is given by r=cosωtx^+sinωty^, where ω is a constant. Which of the following is true?
  1. Velocity and acceleration both are perpendicular to r.
  2. Velocity and acceleration both are parallel to r.
  3. Velocity is perpendicular to r and acceleration is directed towards the origin.
  4. Velocity is perpendicular to r and acceleration is directed away from the origin.

Solution

Position vector is, r=cosωtx^+sinωty^
Velocity of particle is v=drdt
v=-sinωt×ωx^+cosωt×ωy^
v=ω-sinωtx^+cosωty^
Acceleration of the particle is
a=dvdt
a=-ω2cosωtx^+sinωty^
a=-ω2r ,
So direction of r and a are opposite.
As v·a=0va and
v·r=0vr,
So, velocity is perpendicular to r and acceleration is directed towards the origin.

Asked in: NEET 2016 (Phase 1)

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