Physics. PLEASE HELP!!
posted by Amber on .
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

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. 
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?