   Chapter 8, Problem 54P

Chapter
Section
Textbook Problem

A car is designed to get its energy from a rotating solid-disk flywheel with a radius of 2.00 m and a mass of 5.00 × 102 kg. Before a trip, the flywheel is attached to an electric motor, which brings the flywheel’s rotational speed up to 5.00 × 103 rev/min. (a) Find the kinetic energy stored in the flywheel, (b) If the fly-wheel is to supply energy to the car as a 10.0-hp motor would, find the length of time the car could run before the flywheel would have to be brought back up to speed.

(a)

To determine
The kinetic energy stored in the flywheel.

Explanation

Given info: The mass of the flywheel (m) is 5.00×102kg . The radius of the flywheel (r) is 2.00 m. The rotational speed of the flywheel ( ω ) is 5.00×103rev/min

Formula to calculate the kinetic energy is,

KE=12Iω2

• I is the moment of inertia of the flywheel.
• ω is the rotational speed.

The moment of inertia of the flywheel is,

I=12mr2

From the above equations,

KE=14mr2ω2

Substitute 5.00×102kg for m, 2.00 m for r and 5.00×103rev/min for ω .

KE=14(5

(b)

To determine
The required time.

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