# Combined linear and rotational motion question

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

A small solid disk (r<<R), mass m = 9.3 g, rolls on its edge without skidding on the track shown, which has a circular section with radius R = 9.7 cm. The initial height of the disk above the bottom of the track is h = 30.8 cm. When the ball reaches the top of the circular region, what is the magnitude of the force it exerts on the track? (Hint: how fast is it going then?)

**2. Relevant equations**

I = 1/2MR^2

F(centripetal) = (mv^2)/r

**3. The attempt at a solution**

So I’m pretty sure you have to first calculate the velocity of the disk as it enters the circular part. However, I’m confused as to how as we are not provided with a time. Can you assume it is 1 second?

Then the net force must equal the centripetal force at the top of the loop, which will probably be close to zero.

And the speed of the object must match the centripetal force provided by gravity.

so making the centripital force equal to mg gives you

v= sqrt(rg)

I’ve gotten this far, but I have no idea where to go from here. Please help!

http://ift.tt/1nMFIod

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