# Math Help - Angular Momentum

1. ## Angular Momentum

A particle rotates in a circular orbit about a point located 30cm away, with angular speed 2 rad s^-1. If the angular momentum is 0.2 Js, determine the mass of the particle.

I used L=mr^2 omega and got 1.11kg

A constant torque of 0.2Nm accelerates the particle for 5s. Determine the final angular momentum of the particle. I'm not sure how to do this or which equation to use.

2. Originally Posted by PurplePenguin
A particle rotates in a circular orbit about a point located 30cm away, with angular speed 2 rad s^-1. If the angular momentum is 0.2 Js, determine the mass of the particle.

I used L=mr^2 omega and got 1.11kg
ok

A constant torque of 0.2Nm accelerates the particle for 5s. Determine the final angular momentum of the particle. I'm not sure how to do this or which equation to use.
$\alpha = \frac{\tau}{I}$

$L = I\omega_f = I(\omega_o + \alpha t)$

3. Will the moment of inertia still be the same for the second part? Should I calculate it using mr^2?

If I do I get:
I = 0.1
= 0.2/0.1 = 2
L = 0.1(2 + (2 x 5)) = 1.2

Is this correct?

4. Originally Posted by PurplePenguin
Will the moment of inertia still be the same for the second part? Should I calculate it using mr^2?

If I do I get:
I = 0.1
= 0.2/0.1 = 2
L = 0.1(2 + (2 x 5)) = 1.2

Is this correct?
moment of inertia will not change.

calculations are correct ... where are your units?