Shortcut Methods

Shortcut Methods and Tricks to Solve Numerical Problems on Rotational Motion About a Fixed Axis


I. Kinematics

1. Uniform Circular Motion: To find the tangential velocity (v) of a point on the rim of a rotating disk, simply multiply the angular velocity (\omega) by the radius (r) of the disk.

v=ωr


2. Uniform Angular Acceleration: To find the angular displacement (\theta) of a rotating wheel that starts from rest and accelerates uniformly, use the following formula:

θ=12αt2


II. Dynamics

1. Rotational Kinetic Energy: To calculate the kinetic energy (K ) of a rotating disk or wheel, utilize the formula:

K=12Iω2


2. Angular Momentum: Determine the angular momentum (L ) of a rotating wheel, pulley, or other objects employing the equation:

L=12mr2ω

3. Tension in a String: For a rotating pulley with a mass attached to a string, apply the equation

T=mg12mr2α