Chapter 11 review


    Quantitative problems
      Section 11.2
      1. Easy A ball with a mass of 0.5 kg is traveling at 25 m/s and collides with a ball at rest that has a mass of 2 kg. After the collision, both balls are traveling 5 m/s in the same direction. Was momentum conserved?
      2. Calculate the recoil and velocity of the rifle
      3. Easy Calculate the recoil (backward momentum) and velocity of a 4.0 kg rifle that fires a 20 g bullet that travels 1.0 m in 2.15×10-3  s.
      4. Challenging Two carts connected with a compressed spring are placed somewhere along a frictionless track of 4.0 m in length. One cart has a mass of 150 g, and the heavier cart has a mass of 275 g. The spring is released and the two carts move off toward the two ends of the track, reaching the ends at the same instant.
        1. Which cart is initially closer to its end of the track, the light cart or the heavy cart?
        2. If the heavy cart gains a velocity of 2.0 m/s, what is the velocity of the light cart?
        3. How far from its end of the track is the heavy cart placed initially?
        4. How much momentum is produced by the release of the spring?
        5. How much kinetic energy is produced by the release of the spring?
        6. Energy is always conserved. Where does the kinetic energy of the carts come from?
        7. If the compression of the spring is increased, which of these answers a–f will change?
      Section 11.3
      1. A 10,000 kg railroad car traveling north at 10 m/s collides with a 5,000 kg rail car also moving north but at an unknown speed. After the collision, the two cars lock together and move north at 8 m/s. How fast was the second car moving before the impact?
      2. Medium A 2.0 kg puck is moving east at 5.5 m/s. It catches up to and collides with a second identical puck moving due east at 3.0 m/s. The collision is perfectly inelastic.
        1. What is the resulting velocity of the pucks?
        2. What is the initial kinetic energy Eki of the system?
        3. What is the change in kinetic energy, ΔEk, of the system as a result of the collision?
        4. If the mass m is doubled, but the initial velocities are unchanged, does the resulting velocity increase, decrease, or remain unchanged?
      1. A 2,000 kg car moving at 10 m/s collides head-on with a 2,500 kg car moving in the opposite direction at 15 m/s. The two cars are locked together after impact.
        1. Is this an elastic or an inelastic collision? Why?
        2. What is the speed of the cars after impact?
        3. Calculate the kinetic energies of the cars, both before and after impact.
        4. What fraction of the kinetic energy was lost during the impact? Where did the energy go?
      2. Easy A stationary 165 kg football player is tackled by a 178 kg player running at 8 m/s.
        1. How fast are they moving after the collision?
        2. What is the impulse imparted on the stationary player?
        3. What is the impulse imparted on the moving player?
      3. An elastic collision between two balls
      4. Medium In an elastic collision, a 1.0 kg ball moving at 1.0 m/s collides with a 2.0 kg ball moving at −2.0 m/s. The 2.0 kg ball transfers all of its momentum to the 1.0 kg ball.
        1. What velocity does the 1.0 kg ball have after the collision?
        2. What is the initial kinetic energy of the system?
        3. What is the final kinetic energy of the system?
      5. Challenging In an elastic collision involving two balls where one is stationary before the collision, can you make any generalizations about the speed and direction of the two balls after the collision? Consider the situations where (a) the moving ball is more massive than the stationary one; (b) the stationary ball is more massive than the moving ball; and (c) the two balls have equal masses.
      6. Challenging Two clouds collide and form another, more massive cloud. One cloud is stationary, while the other is traveling at 1 m/s. After the collision, the new, combined cloud travels with a velocity of 0.25 m/s. What is the ratio of the masses of the two original clouds?

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