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# Circular Motion Old Spec question Tweet

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1. Circular Motion Old Spec question
This is from an old spec paper and the question has come up twice; Jan03 and June09

In jan03 the answer is D but in june09 the answer is B

Not sure which answer is right and have no idea how to do this :/

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Last edited by X1tinkerbellx; 10-06-2012 at 14:49.
2. Re: Circular Motion Old Spec question
I'd think it was B.

v/r = pi/2

v = 2/5 pi

circumference = 1.6pi

1.6/0.4 = 4

6/4 = 1.5

So it does 1.5 rotations from P in 6 seconds so it ends up exactly opposite P in the circle which is just the diameter 1.6m

Edit: In fact, I just remembered the way I did it first time I saw this question lol, much simpler.

Just count pi/2 6 times from P.

So count 6 quarters from P because pi/2 is a quarter of a circle.
Last edited by justravi; 10-06-2012 at 15:23.
3. Re: Circular Motion Old Spec question
(Original post by justravi)
I'd think it was B.

v/r = pi/2

v = 2/5 pi

circumference = 1.6pi

1.6/0.4 = 4

6/4 = 1.5

So it does 1.5 rotations from P in 6 seconds so it ends up exactly opposite P in the circle which is just the diameter 1.6m

Edit: In fact, I just remembered the way I did it first time I saw this question lol, much simpler.

Just count pi/2 6 times from P.

So count 6 quarters from P because pi/2 is a quarter of a circle.
Thanks!