# Angular momentum; turntable problem

• physicsstdnt
In summary, a 1.7 kg turntable with a diameter of 20cm is rotating at 140rpm on frictionless bearings. Two 480g blocks are dropped onto the turntable simultaneously, sticking to it at opposite ends of a diameter. The question is what the turntable's angular velocity, in rpm, will be after this event. To calculate the moment of inertia, the equation I= .5MR^2 is used, treating the blocks as point masses located at a distance D/2 from the center of rotation. The answer is found by adding the moment of inertia of the turntable and the blocks together, and then multiplying by the final angular velocity.
physicsstdnt

## Homework Statement

A 1.7 kg , 20cm--diameter turntable rotates at 140rpm on frictionless bearings. Two 480g blocks fall from above, hit the turntable simultaneously at opposite ends of a diameter, and stick.

What is the turntable's angular velocity, in rpm , just after this event?

## Homework Equations

L = Iω
Where L is angular momentum.
L_before = L_after

## The Attempt at a Solution

I'm not sure how to calculate the moment of inertia after the masses have landed on the turntable. for the turntable i used the equation I= .5MR^2 . Do I use the same equation for the two additional masses as well and add them to the moment of inertia of the turntable? or simply add the mass to the equation. (.5*(M_table + M_1 + M_2)*R^2)*ω or (I_table + I_m1 + I_m2)ω?

Treat them like point masses located at distance D/2 from the center of rotation.

Thank you sir, that did it

## What is angular momentum?

Angular momentum is a physical quantity that measures the rotational motion of an object around an axis. It is a vector quantity and is defined as the product of an object's moment of inertia and its angular velocity.

## What is the turntable problem in relation to angular momentum?

The turntable problem is a classic physics problem that involves a spinning platform (or turntable) with a mass attached to its edge. The problem explores the concept of angular momentum and how it is affected when the mass is moved closer or further away from the center of the turntable.

## How is angular momentum conserved in the turntable problem?

In the turntable problem, angular momentum is conserved through the principle of conservation of angular momentum. This means that the total amount of angular momentum in a system remains constant, unless an external torque is applied.

## What is the role of moment of inertia in the turntable problem?

Moment of inertia, also known as rotational inertia, is a measure of an object's resistance to changes in its rotational motion. In the turntable problem, the moment of inertia of the turntable and the mass attached to it determines the amount of angular momentum in the system.

## How does changing the distance of the mass from the center of the turntable affect angular momentum?

Changing the distance of the mass from the center of the turntable affects the angular momentum by altering the moment of inertia of the system. As the mass is moved closer to the center, the moment of inertia decreases, resulting in an increase in angular velocity and therefore an increase in angular momentum. Conversely, moving the mass further away from the center increases the moment of inertia and decreases the angular velocity and angular momentum.

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