A car is designed to get its energy from a rotating flywheel with a radius of 1.

Question

A car is designed to get its energy from a rotating flywheel with a radius of 1.85 m and a mass of 575 kg. The flywheel is shaped like a pancake and can be considered as a uniform cylinder. Before a trip, the flywheel is attached to an electric motor, which brings the flywheel's rotational speed up to 4600 rev/min. If the flywheel is to supply energy to the car as would a 9500 Watt motor, find the time (in minutes) the car could run before the flywheel would have to be brought back up to speed.

Explanation / Answer

A car is designed to get its energy from a rotating flywheel with a radius of 2.20 m and a mass of 519 kg.?
Before a trip, the flywheel is attached to an electric motor, which brings the flywheel's rotational speed up to 5150 revolutions per minute. Find the kinetic energy stored in the flywheel.

2) If the flywheel is to supply energy to the car as would a 13.0 hp motor, how long could the car run before the flywheel would have to be brought back up to speed


Firstly, that is a HUGE flywheel- more than half a tonne in a car!

OK, the calculations:
KE=0.5mv^2
=259.5v^2

for circular motion v=rw (w=angular velocity).
the average r is 2.2*2/3=1.47m (approx for circle)
v=1.47x5150/60
v^2=15920
KE=15920*259.5
KE=4MJ (approx)

2) 1HP= 0.735kW (wiki)
and P=KE/t so t=KE/P
t=4000/0.735
t=5400s (2sf) which is roughly an hour and a half.

Hope this helps. Tough problem!

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