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## Homework Statement

A car is designed to get its energy from a rotating flywheel with a radius of 1.85 m and a mass of 678 kg. Before a trip, the flywheel is attached to an electric motor, which brings the flywheel's rotational speed up to 3610 rev/min. Find the kinetic energy stored in the flywheel. Answer in units of J.

If the flywheel is to supply energy to the car as would a 7.9hp motor, how long could the car run before the flywheel would have to be brought back up to speed? Answer in units of h.

## Homework Equations

rotational KE= 1/2 I [tex]\omega[/tex]

^{2}

I=1/2mr

^{2}

[tex]\omega[/tex]=[tex]\omega[/tex]

_{o}+ [tex]\alpha[/tex]t

[tex]\theta[/tex]-[tex]\theta[/tex]

_{o}=[tex]\omega[/tex]

_{o}t+1/2[tex]\alpha[/tex]t

^{2}

## The Attempt at a Solution

I found part 1 which was 82905777.99J but am stuck on how to approach part 2. I think I should use a rotational equation but I don't know angular position nor angular acceleration. Since they give me 7.9hp, I think I should convert it to work (1hp=746W) but don't know what to do with it. Any direction to take would be helpful.