Conservation of Energy Practice Test

The potential energy of a particle moving along the x-axis is given by the function $$U(x) = -4x^3 + 6x^2$$ J, where x is in meters. What is the force on the particle at $$x = -1$$ m?

A roller coaster car of mass $$m$$ travels along a frictionless track with several hills and valleys. Which of the following statements about the work done by the normal force, $$W_N$$, exerted by the track on the car is correct?