Momentum Conservation of Turntable and Beetle System

AI Thread Summary
The discussion revolves around a physics problem involving a beetle walking on a turntable, focusing on the conservation of momentum and angular velocity. The beetle's angular velocity is given as 0.0600 rad/s clockwise relative to the turntable, but the challenge lies in determining its angular velocity relative to an observer. Participants emphasize the need for the turntable's angular velocity to solve the problem, suggesting that the radius can be treated as a variable that cancels out in calculations. The conversation highlights the importance of applying physical equations rather than relying solely on geometric reasoning. Overall, the problem illustrates the principles of momentum conservation in a rotating system.
amb202
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Homework Statement



A beetle with a mass of 30.0 g is initially at rest on the outer edge of a horizontal turntable that is also initially at rest. The turntable, which is free to rotate with no friction about an axis through its center, has a mass of 80.0 g and can be treated as a uniform disk. The beetle then starts to walk around the edge of the turntable, traveling at an angular velocity of 0.0600 rad/s clockwise with respect to the turntable.


a. With respect to you, motionless as you watch the beetle and turntable, what is the angular velocity of the beetle? Use a positive sign if the answer is clockwise, and a negative sign if the answer is counter-clockwise.

b. What is the angular velocity of the turntable (with respect to you)? Use a positive sign if the answer is clockwise, and a negative sign if the answer is counter-clockwise.

c. If a mark is placed on the turntable at the beetle’s starting point, how long does it take the beetle to reach the mark again?


Homework Equations



L= I theta L= mvrsin

The Attempt at a Solution



I know in order to find the angular velocity of the beetle with respect to me, i need to know the angular velocity of the turntable, but without the radius, i cannot figure out how to find this.
 
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Welcome to PF!

Hi amb202! Welcome to PF! :smile:
amb202 said:
A beetle with a mass of 30.0 g is initially at rest on the outer edge of a horizontal turntable that is also initially at rest. The turntable, which is free to rotate with no friction about an axis through its center, has a mass of 80.0 g and can be treated as a uniform disk. The beetle then starts to walk around the edge of the turntable, traveling at an angular velocity of 0.0600 rad/s clockwise with respect to the turntable.
…
I know in order to find the angular velocity of the beetle with respect to me, i need to know the angular velocity of the turntable, but without the radius, i cannot figure out how to find this.

Just call the radius r … you'll find it drops out in the end. :wink:
 
But wouldn't I need the angular velocity of the turntable to figure out the velocity of the beetle with respect to me?
 
Yes, and you can find that from the information given.

This is physics, not geometry …

you can't solve this just with geometry, you need a physical equation also …

which one do you think it is? :smile:
 

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