- #1

lavenderbaby

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## Homework Statement

A 2.1 kg mass is connected to a spring with spring constant k=150 N/m and unstretched length 0.18 m. The pair are mounted on a frictionless air table, with the free end of the spring attached to a frictionless pivot. The mass is set into circular motion at 1.4 m/s. Find the radius of its path.

## Homework Equations

Fs= -kx

Fc= mv^2/r

## The Attempt at a Solution

Since the centripetal force that keeps the mass moving in a circle is provided by the spring, I set Fs = Fc. However, I only equated their magnitudes. Thus, I have this equation:

mv^2/r = kx

r = mv^2 / kx

r = (2.1kg)(1.4m/s)^2 / (150N/m)(0.18m) = 0.15 m

What I am not sure about is the value for x in the equation Fs = -kx. Since the x in the equation is the change in spring length after the spring has been compressed/stretched, the x here should be zero for an unstretched spring. But then, what is the significance of the 0.18 m?

Please let me know if my solution is correct or if I need to change the x.

Thanks in advance!