16 16Ben and Tim race 1 lap around a track. Tim won even though both runners did the same amount of work.
17 Which letter represents the position at which the basketball has the greatest potential energy? Explain. Point C. At this point, which is the highest point, all of the ball’s energy is gravitational potential energy. The ball does not have kinetic energy because it is not moving at this point.17
18 Which letter represents the position at which the basketball has the greatest kinetic energy? Explain. Point E. As the ball falls from C to E, potential energy is converted to kinetic energy. The velocity of the ball increases as it falls, which means that the ball attains its greatest velocity, and thus its greatest kinetic energy, at E. .18
19 Which has the greater kinetic energy, a 10-kg object traveling at a speed of 2 m/s or a 5-kg object traveling at a speed of 4 m/s? Explain. ½ X 10 X 22 = ½ X 10 X 4 = ½ X 40 = 20 Joules ½ X 5 X 42 = ½ X 5 X 16 = ½ X 80 = 40 Joules .19
20 20Is the potential energy of the pendulum increasing or decreasing at position E? Explain. Neither. The potential energy of the pendulum reaches its maximum value at position E, and is neither increasing nor decreasing at that point. .
21 21Compare the sum of the kinetic and potential energies of the pendulum at position A to the sum at position C. (Ignore friction.) Point A is a point of maximum potential energy and minimum kinetic energy. Point C is the point of maximum kinetic energy and minimum potential energy. According to the law of conservation of energy, the sum of the kinetic and potential energies of the pendulum is constant, assuming no losses from friction. So the potential energy at A is equal to the kinetic energy at C. .