A particle is moving in a circle of radius r under the action of a force F = α r 2 which is directed…

A particle is moving in a circle of radius r under the action of a force F=αr2 which is directed towards centre of the circle. Total mechanical energy (kinetic energy + potential energy) of the particle is (take potential energy=0 for r=0):
  1. 56αr3
  2. αr3
  3. 12αr3
  4. 43αr3

Solution

Force F=αr2 will act as centripetal force

αr2=mv2rmv2=αr3

Kinetic energy K.E. =12mv2

K.E.=αr32

Also dU=-F.dr

U=-F.dr

=-αr2-dr

=α0rr2dr

U-0=αr33

U=αr33

So total mechanical energy

E=U+K

=αr33+αr32

E=5αr36

Asked in: JEE Main 2015 (11 Apr Online)

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