Question

Analogue of mass in rotational motion is:
A.) Moment of Inertia
B.) Angular momentum
C.) Gyration
D.) None of these

Answer 1

Hint: Moment of Inertia is defined as the analogue of mass in rotational motion.

Complete step by step answer:
The moment of inertia, otherwise known as the mass moment of inertia, angular mass or rotational inertia, of a rigid body is a quantity that determines the torque needed for a desired angular acceleration about a rotational axis; similar to how mass determine the force needed for a desired acceleration. It depends on the body's mass distribution and the axis chosen, with larger moments requiring more torque to change the body's rate of rotation.
It is an extensive (additive) property: for a point mass the moment of inertia is simply the mass times the square of the perpendicular distance to the axis of rotation. The moment of inertia of a rigid composite system is the sum of the moments of inertia of its component subsystems (all taken about the same axis). Its simplest definition is the second moment of mass with respect to distance from an axis.

Moment of Inertia is defined as the ratio of net angular momentum $L$ of a system to its angular velocity $\omega $ around a principal axis, that is

$I=\dfrac{L}{\omega }$

Note: If the angular momentum of a system is constant, then as the moment of inertia gets smaller, the angular velocity must increase. This occurs when spinning figure skaters pull in their outstretched arms or divers curl their bodies into a tuck position during a dive, to spin faster.