# Homework Help: Circular motion - Edexcel Past Question (Jan 2010)

1. Apr 12, 2012

### jsmith613

1. The problem statement, all variables and given/known data

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

2. Relevant equations

3. 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
thanks

#### Attached Files:

• ###### CircMotionQuestion.doc
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2. Apr 12, 2012

### darkxponent

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