Circular motion - Edexcel Past Question (Jan 2010)

AI Thread Summary
The discussion revolves around a circular motion problem from an Edexcel past exam question, where the task is to show that the radius of the track is 100 meters. The user describes their approach, including drawing a free body diagram and applying relevant equations, but expresses confusion about needing an angle for the calculation. They reference a mass-specific calculation that leads to the conclusion of r = 100m, given a speed of 57 m/s. Other participants confirm the correctness of the calculation, indicating that the initial conclusion is indeed accurate despite the user's uncertainty. The conversation emphasizes the importance of understanding the forces involved in circular motion.
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Homework Statement



I have attached the question that is troubling me including all relevant previous bits of the question along with their answers.

So the question asks me to show the radius of the track is 100m


Homework Equations





The Attempt at a Solution


Obviously I draw a free body diagram with Fnormal vertically upward (as stated) and Fmg vertically downward. The centripetal force acts at a diagonal angle and is hence made by the vertical component force.
to do this calculation I need to know an angle but I don't have one??

The MS calculation is:
4mg - mg (3mg) = mv2/r
hence r = 100m (we have been told the speed is 57 ms-1)
I don't see though how this is correct
please can someone help me
thanks
 

Attachments

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I too think that is correct. I just solved it and got the same answer. Where is the problem?
 

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