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

(a) assume the equation x = at^3 + bt describes the motion of a particular object, with x having the dimension of length and t having the dimension of time. determine the dimensions of the constants a and b. (use the following as necessary: l and t, where l is the unit of length and t is the unit of time.) (b) determine the dimensions of the derivative dx/dt = 3at^2 + b. (use the following as necessary: l and t, where l is the unit of length and t is the unit of time.)