# Circular motion question – finding rpm

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

A 0.60 kg sphere rotates around a vertical shaft supported by two strings, as shown. If the tension in the upper string is 18 N. Calculate

the tension in the lower string?

**the rotation rate (in rev/min) of the system?**

**2. Relevant equations**

v=2(pi)r/T

Fr= mv^2/r

ω = v/R

**3. The attempt at a solution**

I believe I have the first part correct, my question is really about the second part. For the second part of the question: I calculated the x components of each tension force to find the centripetal force = 20.96N. I then found the velocity by rearranging the equation: Fr = mv^2/r to get 3.74m/s. I used the equation ω = v/R to get 9.35 rads/sec and converted it to 89.3 rpm by multiplying 9.35 by 60s and dividing it by 2(pi). Am I on the right track?? Just seems like a small answer

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