# Angular momemtum with a puck and ice cube

1. May 15, 2010

### TsAmE

1. The problem statement, all variables and given/known data

A 100 g puck is attached by a length of string to a 500 g block of ice. The string passes through a hole in the centre of a horizontal, frictionless table, and, because it is revolving in a circle of radius 20 cm, the puck is able to support the ice. (Refer to attachment for pic)

2. Relevant equations

None.

3. The attempt at a solution

I didnt understand this scenario as the whole question was weird. I dont understand how a puck can spin, without being dragged through the centre by the ice cube, since it weighs more and will thus pull puck down. How can this be a momentum problem even if nothing is colliding?

#### Attached Files:

• ###### Momentum.jpg
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2. May 15, 2010

### phyzguy

Think of whirling a ball around on the end of a string. The string will be under tension - this is the centripetal force that keeps the ball moving in a circle. The same thing is happening here - the string is under tension, and that force on the puck keeps it moving in a circle. That same tension is transmitted to the ice cube and holds it up against the force of gravity. Given that, what do you know about angular momentum that will tell you how the system evolves in time?

3. May 15, 2010

### TsAmE

Im not sure, all I know is that the momentum is mass x velocity and angular momentum is mass x velocity x r. I thought momentum had to do with objects colliding.