Angular momentum of puck question

[physics_geek]

Homework Statement

The figure represents a small, flat puck with mass m = 2.41 kg sliding on a frictionless, horizontal surface. It is held in a circular orbit about a fixed axis by a rod with negligible mass and length R = 1.16 m, pivoted at one end. Initially, the puck has a speed of v = 4.72 m/s. A 1.50 kg ball of putty is dropped vertically onto the center of the puck from a small distance above it and immediately sticks to the puck.
a.what is the new period of rotation?
b.Is angular momentum of the puck-putty system about the axis of rotation conserved in this process? choices:
Angular momentum of the puck-putty system is conserved.
Angular momentum of the puck-putty system in NOT conserved.
The pivot exerts a definite torque.
The pivot exerts NO torque.
c.Which statements are true regarding the conservation of mechanical energy of the system in the process?
Some mechanical energy is converted into internal energy.
The collision is perfectly elastic.
The mechanical energy is conserved.
The collision is perfectly inelastic.

Homework Equations

L=Iomega

The Attempt at a Solution

so i don't know how to start part a..any suggestions?

 

[jbsteele]

b. Angular momentum of the puck-putty system is conserved.c. The collision is perfectly inelastic. Some mechanical energy is converted into internal energy.

 

[nlightner]

For part a, we can use the relationship between angular momentum and rotational kinetic energy to solve for the new period of rotation. We know that the initial angular momentum of the puck is equal to its moment of inertia times its initial angular velocity (since it is in circular motion). We can also calculate the final angular momentum of the system after the putty is dropped and sticks to the puck. Since the new system has a larger moment of inertia, the final angular velocity will be smaller. We can then use the relationship L=Iomega to solve for the new angular velocity, and then use that to calculate the new period of rotation.

For part b, the angular momentum of the puck-putty system will be conserved in this process, as there are no external torques acting on the system. The pivot exerts no torque on the system, so the angular momentum will remain constant.

For part c, some mechanical energy will be converted into internal energy in this process, as the collision between the puck and putty is not perfectly elastic. However, overall mechanical energy will still be conserved in the system.