Q1
Two equal and opposite forces acting on a body, not along the same line, constitute a:
📝 SolutionA couple consists of two equal, opposite, parallel forces that do not share the same line of action; it produces pure rotation (torque) without net translational force.
Q2
For a system of particles, the total kinetic energy of a rolling body equals:
📝 SolutionA rolling body has both translational motion of its centre of mass and rotation about that centre, so total KE $= \frac{1}{2}Mv^2 + \frac{1}{2}I\omega^2$.
Q3
The centre of mass of a system of particles moves as if:
📝 SolutionThe centre of mass moves according to Newton's second law applied to the whole system, as though the entire mass were concentrated there and the net external force acted at that point; internal forces do not affect its motion.
Q4
Assertion (A): A ballet dancer spins faster when she pulls her arms and legs close to her body.
Reason (R): Reducing the distance of mass from the axis decreases moment of inertia, and angular momentum is conserved.
Choose the correct option:
Reason (R): Reducing the distance of mass from the axis decreases moment of inertia, and angular momentum is conserved.
Choose the correct option:
📝 SolutionPulling limbs inward reduces $I$; since $L = I\omega$ stays constant with no external torque, $\omega$ must increase, making the dancer spin faster. R correctly explains A.
Q5
Assertion (A): The moment of inertia of a body is not a fixed quantity like its mass.
Reason (R): Moment of inertia depends on the choice of the axis of rotation.
Choose the correct option:
Reason (R): Moment of inertia depends on the choice of the axis of rotation.
Choose the correct option:
📝 SolutionUnlike mass, which is constant, moment of inertia $I = \sum mr^2$ changes with the axis chosen because $r$ (distance from axis) changes. R correctly explains A.
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Class 11 · Physics
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