Posted by **Chan** on Sunday, November 22, 2009 at 10:21pm.

hi,need help please.thank.

A car is designed to get its energy from a rotating flywheel (solid disk) with a radius of 2.00 m and a mass of 525 kg. Before a trip, the flywheel is attached to an electric motor, which brings the flywheel's rotational speed up to 4000 rev/min.

(a) Find the kinetic energy stored in the flywheel.

1 J

(b) If the flywheel is to supply energy to the car as would a 20.0-hp motor, find the length of time the car could run before the flywheel would have to be brought back up to speed.

2 h

physics - drwls, Sunday, November 22, 2009 at 6:58pm

Are those your answers? 1 J and 2 h? How dd you obtain them?

a) Use the formula E = (1/2) I w^2, where w is the angular speed in rad/s and I is the moment of inertia.

(b) Time = (Full speed energy)/Power

You will have to convert horsepower to Watts when using the formula.

I'm sorry I did try to pluck in the number but, it not right could you help me please in part a and b. Greatly appriciate.

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