Which of the following has the most kinetic energy?
a. a bus stopped at a red light
b. a small child moving slowly on a tricycle
c. a player hanging on the rim after dunking a basketball
d. a helicopter getting ready to take off from the top of a tall building

The 5-kg cylinder is initially at rest when it is placed in contact with the wall b and the rotor at a. if the rotor always maintains a constant clockwise angular velocity v = 6 rad> s, determine the initial angular acceleration of the cylinder. the coefficient of kinetic friction at the contacting surfaces b and c is mk = 0.2.

Could someone . i have tried to solve myself but my calculation is off

What is the force that opposes motion and works against the downward pull? a) friction b) gravity c) weight d) acceleration