(Please express your answers in unit vector notation)

- What is the gravitational force on the Earth due to the Sun at this moment?
- What is the angular momentum of the Earth around the Sun at this moment?
- What is the torque due to the Sun's gravitational force on the Earth?
- In about 90 days, the Earth will move about one quarter of the way around the Sun in its orbit. What will its angular momentum around the Sun be at that time?

The Volvo corporation has recently designed a flywheel for its vehicles, which will store some of a car's kinetic energy as it slows at a red light:

Or see the
version on Youtube

The center of the system is a spinning disk in the "Flywheel Module".

The wheel has

- radius
**R = 10 cm** - mass
**M = 5.9 kg** - maximum angular velocity
**60,000 RPM**

- What is the moment of inertia of the flywheel?
- What is the maximum KE the wheel can store?
- The Volvo SE sedan has a mass of
**1600 kg**. Suppose the sedan is rolling at**35 mph**toward a red light. How much KE does the car have? - What fraction of this KE can be stored in the flywheel?
- What is the maximum angular momentum of the flywheel?
- Suppose that, as the car begins to drive again,
the flywheel's angular momentum is transferred to the wheels
over a duration of
**3 seconds**. What is the average torque delivered by the flywheel? - The Volvo SE sedan engine has a nominal torque
of about 266 lb-ft =
**360 N-m**when it is over 1800 RPM. When the car is just staring to move, at, say, 1000 RPM, it might deliver half of that. How much of a boost is the flywheel?

Volvo's flywheel is still in the experimental phase, but it may reduce fuel consumption by a considerable amount in city driving. For more information about Volvo's flywheel, see

- Volvo hybrid drive: 60,000 rpm flywheel, 25% boost to mpg from extremetech.com
- Volvo S60 Flywheel KERS Prototype First Drive from motortrend.com
- Update on status of Volvo's KERS: March 26, 2014

Copyright © Michael Richmond. This work is licensed under a Creative Commons License.