Rotational Motion

Assertion : For a system of particles under central force field, the total angular momentum is conserved. Reason : The torque acting on such a system is zero.

Assertion : A person standing on a rotating platform suddenly stretched his arms. The platform slows down. Reason : This happens as angular momentum is conserved.

A disc of radius $20 \mathrm{~cm}$ and mass $1 / 2 \mathrm{~kg}$ is rolling on an inclined plane. Find out the frictional force such that disc performs pure rolling.

A thin wire of mass $M$ and length $L$ is bent to form a circular ring. The moment of inertia of this ring about its axis is

An elevator starts going up with an acceleration $2 \mathrm{~m} / \mathrm{s}^2$. If radius of the wheel attached to the elevator is $0.1 \mathrm{~m}$, then find out number of revolutions in $10 \mathrm{~s}$?

Assertion : Torque on a body can be zero event if there is a net forces on it. Reason : Torque and force on a body are always perpendicular.

A communication satellite of $500 \mathrm{~kg}$ revolves around the earth in a circular orbit of radius $4.0 \times 10^7 \mathrm{~m}$ in the equatorial plane of the earth from west to east. The magnitude of angular…

Assertion : Value of radius of gyration of a body depends on axis of rotation. Reason : Radius of gyration is root mean square distance of particle of the body from the axis of rotation.

A sphere of mass $10 \mathrm{~kg}$ and radius $0.5 \mathrm{~m}$ rotates about a tangent. The moment of inertia of the sphere is

Assertion : A judo fighter in order to throw his opponent on to the mat tries to initially bend his opponent and then rotate him around his hip. Reason : As the mass of opponent is brought closer to the fighter's hip,…

An air compressor is powered by a $200 \mathrm{rad} / \mathrm{s}$ electric motor using a V-belt drive. The motor pulley is $8 \mathrm{~cm}$ in radius, and the tension in the $\mathrm{V}$-belt is $135 \mathrm{~N}$ on one…

Assertion: The velocity of a body at the bottom of an inclined plane of given height is more when it slides down the plane compared to when it is rolling down the same plane. Reason: In rolling down, a body acquires…