The U.S. Department of Energy had plans for a 1500-kg automobile to be powered c

Question

The U.S. Department of Energy had plans for a 1500-kg automobile to be powered completely by the rotational kinetic energy of a flywheel. The 300-kg flywheel (included in the 1500-kg mass of the automobile) has a 6.0-kgm2 rotational inertia and can turn at a maximum rotational speed of 3600 rad/s.

A) Determine the energy stored in the flywheel at the maximum rotational speed.

B) How many accelerations from a speed of zero to 15 m/s could the car make before the flywheel's energy was dissipated, assuming 100% energy transfer and no flywheel regeneration during braking?

Please help! I have tried this problem several times and cannot figure it out...

Explanation / Answer

A)
energy stored in flywheel = 0.5*I*w^2
= 0.5*6* (3600)^2
= 3.888*10^7 J
Answer: 3.888*10^7 J

B)
energy used up in 1 acceleration = 0.5*m*v^2
= 0.5*1500*(15)^2
= 168750 J

Let number of acceleration be n
n*168750 = 3.888*10^7
n = 230.4
It will make 230 complete accelerations

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