A physics student is sitting on a rotating platform angular velocity question

In summary, a physics student sitting on a rotating platform is holding weights in each of his outstretched hands. He carries out various maneuvers to try to change his angular velocity as requested by his physics instructor. The scenarios described are whether or not his angular velocity changes after performing certain actions. The correct scenarios are: transferring both weights to one hand decreases the angular velocity (FALSE), dropping the weights increases the angular velocity (TRUE), catching a third weight in one hand increases the angular velocity (FALSE), bringing the weights into his chest increases the angular velocity (TRUE). The incorrect scenarios are: transferring both weights to one hand does not change the angular velocity (TRUE), dropping the weights reverses the angular velocity (FALSE), catching a third weight in
  • #1
Kaitlin
2
0

Homework Statement


A physics student is sitting on a rotating platform. He is holding a heavy weight in each of his outstretched hands. At request of his physics instructor(!) he carries out various manoeuvres to try to change his angular velocity. Which of the following scenarios are described correctly?
Select True or False.

Homework Equations


E=1/2(mr^2)w^2

The Attempt at a Solution


1. he transfers both the weights to one outstretched hand. He then stretches his other hand back out to its original position. His angular velocity (after the manouvre is complete) has decreased.
FALSE

2. he transfers both the weights to one outstretched hand. He then stretches his other hand back out to its original position. His angular velocity (after the manouvre is complete) has not changed.
TRUE

3. he drops the weights. His angular velocity increases.
TRUE .

4. he drops the weights. His angular velocity reverses
FALSE

5. A friend throws a third weight so that the student catches it in one of his outstretched hands. No matter what the direction of the throw, the student's angular velocity increases.
FALSE

6. he drops the weights. His angular velocity decreases.
False

7. A friend throws a third weight so that the student catches it in one of his outstretched hands. No matter what the direction of the throw, the student's angular velocity decreases.
TRUE

8. he drops the weights. His angular velocity does not change.
FALSE

9. he raises his feet, and points them outwards from the chair as far as he can. His angular velocity reverses.
False

10. he brings the weights into his chest. His angular velocity increases.
TRUE

I cannot figure out which answer(s) is incorrect
 
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  • #2
I 'm thinking that 3,6 and 8 depend on whether or not the weight lands on the platform ...
 
  • #3
i also tried
False
True
False
False
False
False
True
True
False
True
which is also incorrect
 
  • #4
You could try a true for 6.
 
  • #5
Please provide your reasoning for the dropped weights case (3, 4, 6, 8) and catching the third weight (5,7).
Jilang said:
I 'm thinking that 3,6 and 8 depend on whether or not the weight lands on the platform ...
Why?
 
  • #6
Relevant equation should be angular momentum is conserved. The student can use internal energy to move the weights inwards or outwards, exchanging internal energy for angular kinetic energy. If a weight is thrown by another student, and the student on the spinning platform catches the weight, then a torque impulse occurs, and angular momentum is not conserved since there's an externally sourced torque involved.
 
  • #7
If the weight lands on the platform it will still be rotating and the angular momentum of the platform/student system won't change. Do we know if the students arms extend out over the edge of the platform?

On second thoughts it's irrelevant. Whether or not the angular momentum leaves the system won't affect the rotational velocity.
 
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FAQ: A physics student is sitting on a rotating platform angular velocity question

1. What is angular velocity and how is it related to a rotating platform?

Angular velocity is a measure of the rate at which an object rotates around a fixed point. In the context of a rotating platform, it refers to how fast the platform is spinning.

2. How is angular velocity measured on a rotating platform?

Angular velocity can be measured by dividing the change in the angle of rotation by the change in time. This is usually represented by the symbol ω (omega) and is measured in radians per second (rad/s).

3. How does angular velocity affect a physics student sitting on a rotating platform?

The angular velocity of the platform affects the physics student by causing them to experience centripetal acceleration, which is the acceleration towards the center of the rotating platform. This can make the student feel like they are being pushed or pulled towards the center.

4. What factors can influence the angular velocity of a rotating platform?

The angular velocity of a rotating platform can be influenced by the radius of the platform, the frequency or speed of rotation, and any external forces acting on the platform. Friction and air resistance can also affect the angular velocity.

5. How can the angular velocity of a rotating platform be changed?

The angular velocity of a rotating platform can be changed by increasing or decreasing the frequency or speed of rotation. This can be done manually by the person operating the platform, or by changing the external forces acting on the platform. The radius of the platform can also be changed to affect the angular velocity.

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