Posted by **Amber** on Friday, April 20, 2012 at 12:37pm.

A uniform disk with a mass of 130 kg and a radius of 1.2 m rotates initially with an angular speed of 950 rev/min. A constant tangential force is applied at a radial distance

of 0.5 m.

How much work must this force do to stop the wheel?

Answer in units of kJ

- Physics. PLEASE HELP!! -
**Elena**, Friday, April 20, 2012 at 6:42pm
To stop the wheel, the tangential force will have to do an

amount of work equal to the initial rotational kinetic energy of the wheel.

ω =2•π•n = 2• π•950/60 rad/s

W = I•ω^2/2 = m•R^2• ω^2/4,

where ω =2•π•n = 2• π•950/60 rad/s.

The tangential force and the distance d = 0.5 m are unnecessary for calculation.

- Physics. PLEASE HELP!! -
**Tina**, Wednesday, October 3, 2012 at 5:53pm
a rocket initially at rest on the ground lifts off vertically with a constant acceleration of 2.0 X 10^4 meter per second squared. How long will it take the rocket to reach an altitude of 9.0 X 10^3 meter?

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