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# M2 help- circular motion Watch

1. Hiya. I'm stuck on this M2 question. I'm self teaching so have nowhere to go for help, so I thought I'd ask TSR There's a diagram in my book, but hopefully you can understand it without one. If you do really need it, I’m sure I could somehow scan it in.

The diagram shows a carousel at a fairground. Children are strapped into chairs at the end of the poles 4m long. The poles are hinged at the top to a horizontal drum of radius 3m, which rotates about vertical axis. When the carousel is rotating at full speed, the poles swing out at 20 degrees to the vertical, in vertical planes through the axis of rotation. The mass of the poles is small and can be neglected.

Calculate the time that the carousel takes to make one complete revolution at full speed.

Thanks.
2. I'm doing M2 but this is why I dislike it
SURELY THE TIME IT TAKES DEPENDS ON HOW FAST THE THING CAN SPIN
3. I'm off to watch the apprentice now, but for starters:

The only forces acting on the kids are their weight and the inwards acceleration - these have to balance horizontally. Find the inwards acceleration in terms of the angular velocity (or actual velocity, depending on which formula you prefer), and compare it to the outwards component of the known weight.
4. Still not getting it.
5. What have you got?

Did you figure out the radius of the circular motion?

Have you drawn a diagram with the forces marked on?

Can you get a relationship between the forces mg, and the angle?

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Updated: December 2, 2010

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