Question

A constant torque of 200 N m turns a flywheel, which is at rest, about an axis through its centre and perpendicular to its plane. If its moment of inertia is \(50 \, \text{kg m}^2\), then in 4 second, what will be change in its angular momentum?

• A. \(800 \, \text{kg m}^2/\text{s}\)
• B. \(200 \, \text{kg m}^2/\text{s}\)
• C. \(40 \, \text{kg m}^2/\text{s}\)
• D. \(20 \, \text{kg m}^2/\text{s}\)

Hint:

Angular impulse (\(\tau t\)) directly gives the change in angular momentum.

Answer 1

The Correct Option is A

Step 1: Relation between torque and angular momentum.
Torque is the rate of change of angular momentum: \[ \tau = \frac{dL}{dt}. \]
Step 2: Calculating change in angular momentum.
For constant torque, \[ \Delta L = \tau \, t. \] Given \( \tau = 200 \, \text{N m} \) and \( t = 4 \, \text{s} \), \[ \Delta L = 200 \times 4 = 800 \, \text{kg m}^2/\text{s}. \]
Step 3: Conclusion.
The change in angular momentum is \(800 \, \text{kg m}^2/\text{s}\).