Adapted - AP Physics 1 Unit 6 Review

• Either side of the equation may be used because the mass of the object, the initial speed of the object, and the average force exerted on the object during the collision are known.

• Neither side of the equation may be used because there are too many unknown quantities before, during, and after the collision.

In an experiment, an object is released from rest near and above Earth’s surface. A student must determine the relationship between the direction of the gravitational force exerted on the object and the change in momentum caused by that force. What data could the student collect to determine the magnitude and direction of the gravitational force and the change in momentum of the object? Justify your choices. Select two answers.

• The mass of the object, because it is required to determine the force due to gravity exerted on the object, and the velocity of the object the instant before it reaches Earth’s surface, because it is required to determine the change in velocity of the object.

• The mass of the object, because it is required to determine the force due to gravity exerted on the object, and the distance fallen by the object, because the force is exerted during the entire falling distance.

• The velocity of the object the instant before it reaches Earth’s surface, because it is required to determine the change in velocity of the object, and the acceleration of the object, because it is required to determine the force due to gravity exerted on the object.

• The distance fallen by the object, because the force is exerted during the entire falling distance, and the acceleration of the object, because it is required to determine the force due to gravity exerted on the object.

A student conducts an experiment in which an object travels across a horizontal surface while for 2 s

a net force is applied to a 2 kg

object that initially travels with a speed of 0.5 m/s

. Data collected from the experiment are used to create the graph of the magnitude of the applied force exerted on the object as a function of time is shown. All frictional forces are considered to be negligible. Can the student use the graph and the known data to determine the momentum of the object after the force has been applied?

• Yes, because the average force exerted on the object can be used with the time interval of 2 s

  to determine the change in momentum of the object by using Δp=FΔt

  .

• Yes, because the area bound by the best-fit line and the horizontal axis from 0 s

  to 2 s

  can be used to determine the change in momentum of the object.

• No, because the data is too scattered to determine the average force that is exerted on the object.

• No, because the student needs to know the direction that the force is applied to the object because the applied force will be in the same direction as the change in momentum of the object.

Answer explanation

The change in momentum has a direction because it is a vector quantity. The graph does not indicate the direction that the force is applied to the object. If the direction of the change in momentum is not known, the student cannot use the data to determine the final momentum of the object

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LO.3.D.1.1

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• Only equation 1, because the momentum lost by cart A

  is gained by cart B

  . This change in momentum can be determined using the graph.

• Only equation 2, because the force is exerted only on cart B

  , so there is no information about the force exerted on cart A

  .

• Equation 1 and equation 2, because the system is closed and all quantities are known except for the final speed of cart A

  .

• Neither equation, because there are too many unknown quantities.

Answer explanation

Correct. The known masses of both carts and the initial speed of cart A

, along with information shown in the graph, can be used in equation 1 to determine the final speed of cart A

. The masses of both carts, the initial speeds of both carts, and the final speed of cart B

are known. Therefore, equation 2 can also be used to determine the final speed and direction of cart A

.

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Two objects stick together and move with a common velocity after colliding. Identify the type of collision.

• Explosion

• Impulse

• Perfectly inelastic

• Elastic

A billiard ball collides with a stationary identical billiard ball in an elastic head-on collision. After the collision, which of the following is true of the first ball?

• it maintains its initial velocity

• it has one-half its initial velocity

• it comes to rest

• it moves in the opposite direction

Answer explanation

Since both balls are identical, they have the same mass. In an elastic collision, kinetic energy is conserved, therefore once they collide, the second ball will inherit the first ball's Kinetic Energy, and the first ball will come to rest.

What is the the total momentum of the red and blue ball before the collision?

• 16 kg m/s

• 32 kg m/s

• 2 kg m/s

• 6 kg m/s

While playing pool, the white cue ball strikes the 8-ball in an elastic collision. Before the collision, the cue ball's velocity was 10 m/s and the 8-ball was at rest. If both ball's have a mass of 0.15 kg and the cue ball's velocity after the collision is 2 m/s, what is the 8-ball's velocity?

• 2 m/s

• 8 m/s

• -2 m/s

• 1.5 m/s

Answer explanation

On the left-hand side of the equation, only the 2 kg mass and its final speed after the collision are known. The average force exerted on the 2 kg object from the 1 kg object should be considered. Therefore, the initial speed of the 2 kg object can be determined using these substitutions.

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Ball X of mass 1.0kg and ball Y of mass 0.5kg

travel toward each other on a horizontal surface. Both balls travel with a constant speed of 5m/s until they collide. During the collision, ball Y exerts an average force with a magnitude of 40N for 16 s on ball X. Which of the following best predicts ball Y's momentum after the collision?

• Ball Y will travel at a speed less than 5m/s

  in the same direction of travel as before the collision.

• Ball Y will travel at a speed less than 5m/s in the opposite direction of travel as before the collision.

• Ball Y will travel at a speed greater than 5m/s in the opposite direction of travel as before the collision.

• Ball Y's motion cannot be predicted because the impulse on it is not known.

Answer explanation

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