Maximizing Flywheel Energy and Power for Passenger Bus Design

[Mitchlan]

Homework Statement

In the design of a passenger bus, it is proposed to derive the motive power from the energy stored in a flywheel. The flywheel, which has a moment of inertia of 4.0 x 102 kgm2, is accelerated to its maximum rate of rotation of 3.0 x 103 revolutions per minute by electric motors at stations along the bus route.
a) Calculate the maximum kinetic energy that can be stored in the flywheel.
b) If, at an average speed of 36 kilometres per hour, the power required by the bus is 20 kW, what will be the maximum possible distance between stations on the level?

The Attempt at a Solution

Part A:

K (Rot)Energy = 1/2 I omega^2
= 1/2 * 4 * 10^2 * 314.159^2
= 68.832 kJ


Part B:

Please help: do I need to find torque and angular displacement, use this to find work then distance?


Any nudge in the general direction greatly appreciated. Thanks in advance.

 

[rock.freak667]

The bus requires 20kW or 20 kJ/s, so for how long will 68.832 kJ carry it?

That will give you a time, and you are given a speed of 36 km/h so you can get distance.

 

[Mitchlan]

The bus requires 20kW or 20 kJ/s, so for how long will 68.832 kJ carry it?

That will give you a time, and you are given a speed of 36 km/h so you can get distance.

Great! Thanks for that!