Section 1 review
The law of conservation of energy states that energy cannot be created or destroyed—only transformed. More specifically, the total energy remains constant in a closed system. An object’s mechanical energy is defined as the sum of its potential and kinetic energies, and it may remain constant in the absence of “frictional losses.” Read the text aloud
system, closed system, open system, law of conservation of energy, state

E initial = E final
E p + E k =constant

Review problems and questions

  1. You shoot a 2.0 kg basketball toward the hoop with an initial total energy of 500 J. (Neglect air friction on the ball.)
    1. When the ball reaches the top of its arc, what is its total energy?
    2. When the ball is just about to hit the rim, what is its total energy?
    3. What principle are you demonstrating? Read the text aloud Show
A ball shortly after being tossed upwrd
  1. Panel A shows a ball shortly after being tossed upward. Panel B shows the same ball at an instant on its way back down. Assume that air resistance can be ignored. Which statement is true?
    1. The potential and kinetic energy are both greater in Panel A than in Panel B.
    2. The potential and kinetic energy are both greater in Panel B than in Panel A.
    3. The potential energy is greater in Panel A, but the kinetic energy is greater in Panel B.
    4. The potential energy is greater in Panel B, but the kinetic energy is greater in Panel A. Read the text aloud Show
Roller coaster on a track
  1. A roller-coaster cart, initially stationary at position a, is given a gentle push to the right. As it glides along the track, it passes through positions b, c, and d. Assume that friction and air resistance can be ignored.
    1. At which of the four positions is gravitational potential energy greatest?
    2. At which position is the cart moving fastest?
    3. At which position(s) is/are potential and kinetic energy equal? Read the text aloud Show
  1. A ball is dropped from two heights, one four times as high as the other. What is the ratio of the speeds in the two cases just before the ball hits the ground? (Assume that air resistance can be ignored.) Read the text aloud Show

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