8. a boy pulls a 20.0-kg box with a 140-n force at 30° above a horizontal surface. if the coefficient of kinetic friction between the box and the horizontal surface is 0.25 and the box is pulled a distance of 28.0 m, what is the net work done on the box?

(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.)