Section 3 review
There are two basic categories of collisions, elastic and inelastic. Momentum is conserved in both types of collisions. Kinetic energy, however, is conserved only in elastic collisions. Kinetic energy isn’t really lost during inelastic collisions; it is converted into other forms of energy, such as thermal energy or sound. In a perfectly inelastic collision, the colliding objects stick together and move as a single body. Read the text aloud
collision, inelastic collision, elastic collision

m 1 v i1 + m 2 v i2 = m 1 v f1 + m 2 v f2
1 2 m 1 v i1 2 + 1 2 m 2 v i2 2 = 1 2 m 1 v f1 2 + 1 2 m 2 v f2 2

Review problems and questions

  1. Rudolf is traveling at 3.0 m/s in his toy bumper car when he has a rear-end collision with Marcel, whose bumper car is initially at rest. The mass of each boy and his bumper car is 100 kg. As a result of the collision, Marcel glides off at 3.0 m/s in the direction that Rudolf had been going.
    1. What is Rudolf’s velocity after the collision?
    2. Is the collision elastic or inelastic? Read the text aloud Show
  1. A collision takes place on a hockey rink. Sonja (m = 80 kg) slides into Yoon-Hee (m = 60 kg), who is initially at rest. Sonja skates into Yoon-Hee at 3 m/s, and as a result Yoon-Hee is ejected with the same velocity, in the direction that Sonja had been going.
    1. What is Sonja’s velocity after the collision?
    2. Is the collision elastic or inelastic? Read the text aloud Show
Three collision scenarios
  1. The graphic above shows three collision scenarios (A, B, and C). Each collision is between two objects that only can move horizontally. Match each scenario with one of the numbered statements (I, II, III, or IV). Read the text aloud Show

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