8.PS2.3 Kinematics

Which of the following graphs represent objects demonstrating changes in position? (Select 2 choices)

• A

• B

• C

• D

You throw a ball directly upwards to the ceiling. It travels up, slows down, reverses direction, and falls to the floor. Which of the following statements about the ball’s motion must be true?

• The acceleration increases as it approaches the ceiling but decreases near the floor.

• The acceleration is smallest just before it hits the floor.

• After the ball leaves your hand, acceleration is constant until the ball hits the floor.

• The acceleration is the smallest as the ball approaches the ceiling.

The graph below is about a car in Newport, Tennessee during a 60-minute period. Describe the motion of the car during this time period, and explain what must happen to change the car’s motion.

• The car is stationary during this time. To change the car’s motion, it would have to be acted upon by unbalanced forces.

• A distance vs. time graph will not give the information needed to determine the motion of the car. A speed vs. time graph will be needed instead.

• The car is traveling at a constant speed. To change the car’s motion, it would have to be acted upon by horizontal forces.

• The car is increasing in speed. It shows a horizontal line, so it must be driving down a straight road. To change the car’s motion, it would have to be acted upon by net force.

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A car traveling to the West begins to slow down as it approaches a traffic light.

Which statement concerning the motion of the car is correct?

• The car’s acceleration is negative. The car’s velocity is also negative.

• The car’s acceleration is positive. but the velocity is negative

• The car’s acceleration is positive. The cars velocity is also positive.

• The acceleration of the car is negative, but the velocity is positive.

Examine the following information about an object in motion.

Two-Part Question

Part One: Describe the motion of the free-falling object show above.

Part Two: What force changes would have to occur to make this object hover?

• Part One: It is accelerating upward due to unbalanced forces acting on the object.

  Part Two: The downward force must decrease by 400 N to make this object hover.

• Part One: The object is accelerating in an upward direction due to unbalanced forces.

  Part Two: The upward force must be decreased by 600 N to make this object hover.

• Part One: It is accelerating downward due to unbalanced forces acting on the object.

  Part Two: The forces above and below the object would have to be equal (balanced).

• Part One: The object is falling at a constant speed downward due to balanced forces.

  Part Two: The force below the object must be increased by 200 N.

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Examine these two free-body diagrams of a car in motion.

Contrast the motion of the car in these two diagrams, and select the correct cause and effect description about the first diagram.

• In diagram 01 the car is moving vertically. In diagram 02 the car is not moving.
  Cause: In the first diagram there is 100N of upwards force.
  Effect: The car in the first diagram will move vertically.

• In diagram 02 the car is stationary. In diagram 01 the car is moving forward.
  Cause: In the first diagram there is horizontal motion but no vertical motion.
  Effect: This horizontal motion will stop the car from moving vertically.

• In diagram 01 the car is moving backwards. In diagram 02 the car is stationary.
  Cause: In the first diagram there is 100N of force to the right.
  Effect: Therefore the car in the first diagram will move backwards

• In diagram 01 the car is stationary. In diagram 02 the car is moving forward.
  Cause: In the second diagram there is no vertical motion.
  Effect: Therefore the car in the second diagram also has no horizontal motion.

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n 1969 astronauts first traveled to the Moon in the Saturn-5/Apollo spacecraft. This rocket ship blasted off from the launch pad in Florida and was propelled with ever increasing speed upwards through the Earth’s atmosphere flying towards the Moon. Which one of the following graphs best represent the motion of this rocket ship after it blasted off from the launch pad?

• A

• B

• C

• D

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A basketball player shoots a free-throw. The motion of the basketball is shown. Describe the motion of the basketball after it leaves the player’s hands, and explain how this is an example of acceleration.

• The ball travels in a curved trajectory in two directions with decreasing speed. This is acceleration because of the change in direction.

• The ball moves downwards and then upwards in an arc. This is acceleration because of the change in force pulling the ball downwards.

• The ball travels in a horizontal line to the basket with increasing speed. This is acceleration because of the change in velocity.

• The ball travels in curved trajectory in a single direction with decreasing speed. This is acceleration because of the change in velocity.

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Two students are pushing a cart as shown in the diagram.

Two-Part Question

Part One: Identify the magnitude and direction of the cart’s motion.

Part Two: How is this an example of the crosscutting concept called stability and change.

• Part One: The cart will accelerate to the right with a magnitude of 150 N.

  Part Two: When unbalanced forces act on an object, its position is stable. When balanced forces act on an object, the position of the object changes.

• Part One: The cart will accelerate to the left with a magnitude of 550 N.

  Part Two: When balanced forces act on an object, its position is stable. When unbalanced forces act on an object, the position of the object changes.

• Part One: The cart will accelerate to the right with a magnitude of 50 N.

  Part Two: When balanced forces act on an object, its position is stable. When unbalanced forces act on an object, the position of the object changes.

• Part One: The cart will accelerate to the right with a magnitude of 350 N.

  Part Two: When balanced forces act on an object, its position is stable. When unbalanced forces act on an object, the position of the object changes.

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