Chapter 11 review


    Conceptual questions
      Section 11.1
      1. Medium How is it possible that two objects with the same mass could have the same kinetic energy but different momenta?
      Section 11.2
      1. When two identical pucks collide on a frictionless surface, the impulses they receive are always equal in magnitude and opposite in direction.
        1. Why must this be true? Explain this using Newton’s third law of action and reaction.
        2. If the pucks are of unequal mass, and the surface is not frictionless, then are the impulses on the pucks from the collision still equal?
      2. Explain how you would use two frictionless carts with a spring between them to demonstrate momentum conservation.
      3. Give a five-slide oral presentation describing how the concept of momentum conservation applies to a jet engine. Your presentation should use the following terms: “exhaust velocity,” “mass,” and “forward momentum.”
      4. Easy Two ballistic carts have a compressed spring between them, such as in Investigation 11A on page 621. If one cart is much more massive than the other, which one will have a greater speed after the carts are released?
      5. Medium What physical principle would suggest it is a bad idea to jump forward off of a skateboard without putting one foot on the ground while you jump?
      6. Medium A stationary package on a frictionless surface explodes into two chunks. One chunk has mass M, and the other chunk has mass 2M.
        1. What is momentum of the system before the explosion?
        2. What is momentum of the system after the explosion?
        3. The smaller chunk moves due north with a speed of 10 m/s. Describe the motion of the larger piece.
      7. Challenging Two students are arguing about the following situation:
        A girl is traveling at constant speed in a frictionless cart. She has a supply of baseballs with her. What happens to the velocity of the cart if she starts dropping the baseballs over the side?
        Jamal argues that the velocity of the cart does not change. Samuel says that momentum is conserved, so the cart must speed up as its mass decreases. Who is right?
      1. Easy How can you demonstrate the law of conservation of momentum using a billiards table and any additional equipment you need?
      Section 11.3
      1. Jorge is conducting an investigation into perfectly inelastic collisions using equipment where two carts collide with each other. He can set up the carts either to bounce off each other or to stick together upon impact. Which setting should he use?
      2. Easy Two football players collide head on. The momentum of each player changes after the collision. Is momentum conserved?
      3. Easy How does solving an elastic collision problem differ from solving an inelastic collision problem?
      4. Medium An action hero jumps out of a stationary helicopter onto a car moving on an icy lake. What happens to the velocity of the car when the hero lands on it?
      5. Medium The bumpers on cars, as well as some cars’ engine compartments, are designed to collapse in a collision. Why is this a useful design?
      6. Medium Two unknown objects collide. If one of the objects is stationary before the collision, can both objects be stationary afterward? Can only one be stationary afterward?
      7. Medium If two objects collide and one is stationary before impact, can only one of the two objects be stationary after impact? Justify your answer.
      8. Medium When two pucks undergo a perfectly inelastic collision, which statement below is always true about the total kinetic energy Ek of the pucks?
        1. Ek after the collision will be less than Ek before the collision.
        2. Ek after the collision will be greater than Ek before the collision.
        3. Ek after the collision will be zero.
        4. Ek after the collision will equal Ek before the collision.
      9. Challenging In an elastic collision, a tennis ball hits a rigid wall and bounces back with a momentum that is equal in magnitude and opposite in direction. The wall is rigidly fixed to its surroundings. Is momentum conserved? Explain.
      10. Challenging Two identical balls collide head on, while traveling at the same speed, but in opposite directions. The two balls come to a complete stop as a result of the collision. Is the collision elastic or inelastic? Why or why not?

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