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Rotational kinetic energy of a flywheel

  • Thread starter mfm578
  • Start date
  • #1
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Homework Statement


A car is designed to get its energy from a rotating flywheel with a radius of 1.12 m and
a mass of 736 kg. Before a trip, the flywheel is attached to an electric motor, which
brings the flywheel’s rotational speed up to 7270 rev/min.
Find the kinetic energy stored in the fly-wheel.
Answer in units of J.

Homework Equations


KE = 0.5*Inertia*w^2
Inertia = m*r^2


The Attempt at a Solution



convert 7270 rev/min to rad/s = 761.314 rad/s

KE equation: 0.5*(761.314)^2*(736 kg)*(1.12m)^2 = 267554029.7

answer is apparently wrong... help please?




PART 2, I don't think I can do this without a correct answer from part 1

If the flywheel is to supply energy to the car as would a 11.8 hp motor, how long could the
car run before the flywheel would have to be brought back up to speed?
Answer in units of h.
 

Answers and Replies

  • #2
45
0
Is it possible the flywheel is modeled as a disk rather than a hoop, in which case

I = .5MR^2, not I = MR^2 ?
 
  • #3
ehild
Homework Helper
15,409
1,813
Yes, try!

ehild
 

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