CHAPTER 4 DRILL
- A Since the force F is perpendicular to the displacement, the work it does is
zero.
- B By the work–energy theorem
- B Since the box (mass m) falls through a vertical distance of h, its
gravitational potential energy decreases by mgh. The length of the ramp is
irrelevant here.
- A W = ∆K = −∆U. The gravitational force points downward while the book’s
displacement is upward. Therefore, the work done by gravity is −mgh = −(2
kg)(10 N/kg)(1.5 m) = −30 J.
- D First, the kinetic energy the block gains is the same as the potential energy it
loses, which is mgh. Since this is equal to mv^2 , we find that v =.
Plugging in g = 10 m/s^2 and h = 4 m, we get v = ≈ 9 m/s.
- C Apply conservation of mechanical energy (including the negative work done
by Ff, the force of sliding friction).
