Quantrex Quantrex AcademyJEE · NEET · NDA PYQs with solutions Open app
JEE Main202125 Jul 2021Morning ShiftPhysicsRotational MotionActual

Given below are two statements: one is labelled as Assertion A and the other is labelled as Reason R. Assertion A: Moment of inertia of a circular disc of mass M and radius R about X , Y axes (passing through its plane) and Z-axis which is perpendicular to its plane were found to be I x , I y and I z , respectively. The respective radii of gyration about all the three axes will be the same. Reason R: A rigid body mak

Options

  1. ABoth A and R are correct but R is not the correct explanation of A.
  2. BA is not correct but R is correct.
  3. CA is correct but R is not correct.
  4. DBoth A and R are correct and R is the correct explanation of A.

Correct answer

B. A is not correct but R is correct.

Step-by-step solution

I z = I x + I y (using perpendicular axis theorem) and I = m k 2 ( K : radius of gyration) so m K z 2 = m K x 2 + m K y 2 K z 2 = K x 2 + K y 2 So radius of gyration about axes x , y and z will not be same, hence assertion A is not correct reason R is correct statement (property of a rigid body).

Practice Rotational Motion on Quantrex Academy →

More from Rotational Motion

Consider a large disk of radius R and two smaller disks, each of radius r = R/50 , lying on its circumference, as shown in the figure. The smaller disks are initially in contact wi 2026A solid cylinder of radius R rolls without slipping with a center of mass speed v₀ = gR 3 on a horizontal surface with a vertical edge, as shown in the figure. Here, g is the accel 2026List-I shows four planar structures made of uniform solid rods each of mass m and length l . In the List-II the possible moment of inertia of these structures about an axis OCO' , 2026Passage: A uniform circular disk of radius 0.2 m and mass 1 kg is pivoted at its top point C such that it can rotate freely around C in the XY plane, as shown in the figure. Initia 2026Passage: A uniform circular disk of radius 0.2 m and mass 1 kg is pivoted at its top point C such that it can rotate freely around C in the XY plane, as shown in the figure. Initia 2026A solid cylinder having radius R and length L is slipping on a rough horizontal plane. At time t=0 the cylinder has a translational velocity v₀=49 m/s, perpendicular to its axis an 2026A solid sphere ( A ) of mass 5m and a spherical shell ( B ) of mass m , both having same radius, are placed on a rough surface. When a force of same magnitude is applied tangential 2026A solid sphere of radius 4 cm and mass 5 kg is rotating (rotation axis is passing through the centre of the sphere) with an angular velocity of 1200 rpm. It is brought to rest in 1 2026 Full Rotational Motion list All JEE Main PYQs