Collision

The law of conservation of momentum also allows us to analyse collisions between objects
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Questions #: 5
Time: 10 minutes
Pass Score: 80.0%
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One pool ball colliding

 

Consider the simple case of one pool ball colliding head-on with another at rest.  Before the collision, the system's total momentum is the product of the mass of the moving ball and its velocity.  Those of you who have played pool know what happens after such a collision:  the ball that has been moving stops, and the other ball moves forward.  The conservation of momentum can tell us what the speed of that second ball must be.

  1. Assuming their masses to be the same, how does the momentum of the second ball after collision compare to that of the first ball before collision? (1) transparent
  2. How does the velocity of the second ball after collision, compare to the initial velocity of the first ball? (2) transparent
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They are equal
First ball is greater
Second ball is greater
POINTS (1)

Correct Answer

Explanation

Car wreck

Consider a wreck in which a car runs into the back of a stationary truck.  Before the collision, the car has momentum forward.  We will suppose that the car and truck stick together after the crash.

The law of conservation of momentum tells us what the momentum of the wreckage will be.

  1. What will it be equal to? (1) transparent
  2. What values would we need to know to calculate the velocity of the wreckage after impact? (2) transparent
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the momentum of the car before collision
the momentum of the car after collision
masses of car and truck, and pre-wreck velocity of the car
masses of car and truck, and pre-wreck velocity of the truck
POINTS (1)

Correct Answer

Explanation

Since momentum is the product of a vector and a scalar, momentum is also a vector

POINTS (1)

Correct Answer

Explanation

If ball A moves towards the right, what does the law of conservation of momentum tell us about the motion of the ball B after the collision?

 

collision_ball_explained.gif

POINTS (1)

Correct Answer

Explanation

Total of vectors

In part 3, of the figure, arrow XA, which represents the sideways momentum of A after collision, must be the same length as arrow XB, representing ball B's sideways momentum.  Vector YA and YB represent the downward momenta of balls A and B.

The total of these two vectors must equal what momentum?

POINTS (1)

Correct Answer

Explanation

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± RND C = MC

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