Section 2 review
Newton’s third law states that any two interacting objects push or pull each other with equal (and opposite) force. One key consequence of Newton’s third law is that the total momentum of any closed system is conserved (does not change). If two objects push each other away, their individual momenta change by equal amounts, though in opposite directions, resulting in a zero net change in the momentum of the system. Conservation of momentum forms the basis for understanding rocketry, jet propulsion, and the recoil motions of guns and cannons. Read the text aloud
law of conservation of momentum

Review problems and questions

  1. The law of conservation of momentum applies to closed systems. What does the term “closed system” mean in this context?
    1. No force of any kind can act upon any object within the system.
    2. No net force can act upon any object within the system.
    3. No net force may operate upon the system from outside the system. Read the text aloud Show
  1. Jaime and Ayesha stand motionless while wearing roller skates. They gently press on each others’ hands, palms up. Each friend then rolls away at a speed of 0.8 m/s. Which statement accurately compares their masses?
    1. Jaime and Ayesha have equal masses.
    2. Jaime is more massive than Ayesha.
    3. Jaime is less massive than Ayesha.
    4. There is not enough information to compare their masses. Read the text aloud Show
  1. During a spacewalk, Dmitri finds himself floating 3 m from his space station’s airlock. He only has one minute of air left. He has one detachable 10 kg toolkit, which he can toss to propel himself toward safety.
    1. How fast will he need to move to reach the airlock before he runs out of air?
    2. Dmitri and his space suit together have a mass of 100 kg. How fast must he throw the toolkit to propel himself toward the airlock at the required speed (found in the previous step)? Read the text aloud Show
  1. During the spacewalk described above, Dmitri tosses his detachable 10 kg toolkit. The statements below refer to Dmitri and the toolkit during the throw. Decide whether each statement is true or false.
    1. The magnitude of the force is the same for each.
    2. The duration of the event is the same for each.
    3. The magnitude of the acceleration is the same for each.
    4. The magnitude of the impulse is the same for each. Read the text aloud Show

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