Turntable Rotation with weight on edge v. in the center

• AROD
In summary: I also calculated his angular momentum pre-walk as 0 and post-walk as I*ω so his angular momentum changes by 0.5.
AROD

Homework Statement

A man (mass m1 = 100 kg) stands at the fringe of the large rotary table (radius R = 5 m, massm2 = 100 x m1), which rotates at a frequency of 10/min. The man goes along a radius line towards the table center until he reaches the rotation axis. The spatial extent of the man should be neglected.
a) How does the rpm (revolutions per minute) number of the rotary table change (in absolute
und relative terms)?
b) The man has to work against the centrifugal force in order to get to the center of the table.
Show that the work done by the man amounts to the increase of the rotational energy of theentire system.

Homework Equations

conservation of momentum: p = p1 + p2
rotational energy : 1/2mr^2w^2

The Attempt at a Solution

Period of 36s with man on edge. How is it different when he is in the middle?

Your angular momentum can be expressed as I*ω

So won't your I*ω before = I*ω after?

Figure then your I with the 1kg at the edge and 1 kg at the center.

I before = 1/2m*(5)2 + 1*52

What is it after his walk? Then you can figure what happens to ω can't you?

How is it different when he is in the middle?
It's not if a motor is maintaining the 10 RPM.
On the other hand, if we have no motor, the thing will speed up as the man's mass moves toward the center like a skater spins faster when his arms are held closer. Maybe you are supposed to use conservation of angular momentum to figure this out.

moment of inertia for this disk is 1/2*(mass disk)*r^2 and before with the man on the edge the total inertia is plus also 1/2*(mass man)*(position)^2 ?

and at the end the man is in the center so his distance from center of mass is 0 and doesn't contribute to the intertia, just the total mass

That looks great, Arod. I think Lowly Pion typoed the mass of the man in his message.

Delphi51 said:
That looks great, Arod. I think Lowly Pion typoed the mass of the man in his message.

Sort of. I calculated it as the turntable being 100 and the man as 1 according to the 100:1 and dropped out m1. My typo really was in not relating that step.

1. What is the difference between turntable rotation with weight on edge and in the center?

The main difference between these two types of turntable rotation is the distribution of weight. When a weight is placed on the edge of the turntable, it creates an off-center rotation, whereas placing the weight in the center creates a balanced, central rotation.

2. How does the placement of weight affect the speed of rotation on a turntable?

The placement of weight can affect the speed of rotation on a turntable. When the weight is on the edge, the turntable will rotate faster due to the uneven distribution of weight. When the weight is in the center, the rotation will be slower and more controlled.

3. Does the placement of weight on a turntable affect its stability?

Yes, the placement of weight can affect the stability of a turntable. When the weight is on the edge, the turntable may be more prone to wobbling or tipping over. When the weight is in the center, the turntable will be more stable and less likely to tip over.

4. Are there any benefits to using turntable rotation with weight on edge?

Yes, there are some potential benefits to using turntable rotation with weight on edge. This type of rotation can create a faster spinning motion, which may be desirable for certain experiments or demonstrations. It can also create a more dramatic visual effect.

5. Which type of turntable rotation is better for scientific experiments?

The type of turntable rotation that is better for scientific experiments will depend on the specific experiment being conducted. In general, using a turntable with weight in the center will provide a more controlled and stable rotation, which may be preferable for precise measurements. However, turntable rotation with weight on edge may be more suitable for experiments that require a faster spinning motion or a visual effect.

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