# Moment of Inertia/ Kinetic Energy

A flywheel is a solid disk that rotates about an axis that is perpendicular to the disk at its center. Rotating flywheels provide a means for storing energy in the form of rotational kinetic energy and are being considered as a possible alternative to batteries in electric cars. The gasoline burned in a 260-mile trip in a typical midsize car produces about 1.3 x 10 9 J of energy. How fast would a 20-kg flywheel with a radius of 0.34 m have to rotate in order to store this much energy? Give your answer in rev/min.

I= 1/2mr squared
J= 1/2 IW squared

.5*20*(.34*.34)
I=1.156
1.3 X 10 9 = .5 x 1.156 x W squared
W=47425.04558

My speed is obviously incorrect. I do not understand where the distance (260 mile trip) comes into play in this problem

## Homework Statement

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.5*20*(.34*.34)
I=1.156
1.3 X 10 9 = .5 x 1.156 x W squared
W=47425.04558
OK. What are the units of ω? You'll need to convert from those standard units to the requested units of rev/min.
I do not understand where the distance (260 mile trip) comes into play in this problem
It doesn't. It's just there to provide some background information so the problem seems realistic.

okay i got it. thanks