Quantrex Quantrex AcademyJEE · NEET · NDA PYQs with solutions Open app
KCET2026PhysicsRotational Motion

If the earth were to suddenly contract to half of its present radius, what would be the duration of the day?

Options

  1. A6 h
  2. B18 h
  3. C24 h
  4. D30 h

Correct answer

A. 6 h

Step-by-step solution

By the principle of conservation of angular momentum, the angular momentum of the Earth remains constant since no external torque acts on it. I₁ ₁ = I₂ ₂ 2 5 M R^2 ( 2 T₁ ) = 2 5 M ( R 2 )^2 ( 2 T₂ ) R^2 T₁ = R^2 4 T₂ T₂ = T₁ 4 Given T₁ = 24 h, we get: T₂ = 24 4 = 6 h Answer: 6 h

Practice Rotational Motion on Quantrex Academy →

More from Rotational Motion

A bullet, fired into a door gets embedded exactly at it's centre, causing the door to rotate about it's vertical axis, practically without friction, with an angular velocity of 0.6 2026A singer, during his performance, stands on the edge of a circular turntable, and begins to walk along its edge with a speed of 1.5 ms⁻¹ relative to the ground. The turn table is m 2026A particle starts rotating from rest. The instantaneous angular displacement is = 3t^3 - t^2 , where is in radian and t in s; The angular velocity at t = 1 s is 2026Four masses each 2 kg are placed at the corners A, B, C, D of a mass less square frame. 40 kg mass is at the centre O of a square frame of side 0.2m. It is to be rotated about an a 2026The position of a particle of mass 1 kg at time t is given by r = t , i + j + 2t^2 , k , where t is in seconds and the coefficients have the proper units for r to be in metres. Wha 2026The angular momentum of a moving body remains constant, if 2026The angular velocity of a body changes from 6 rad s ⁻¹ to 21 rad s ⁻¹ in a time of 1.5 s. If the moment of inertia of the body is 100 ~g ~m ^2 , then the rate of change of angular 2025The moment of inertia of a solid cylinder of mass 2.5 kg and radius 10 cm about its axis is 2025 Full Rotational Motion list All KCET PYQs