Dynamics

Which force diagram shows the forces on a skydiver who is slowing down immediately after her parachute opens?

• A

• B

• C

• D

Which of the following must be true if an object is accelerating?

• It is going really fast.

• It is moving away from the frame of reference point.

• Balanced forces are acting upon it.

• Unbalanced forces are acting upon it.

A student drops a ball onto the floor and it bounces. Which of the following statements about the interaction between the ball and the floor is correct?

• The floor applies the same amount of force to the ball that the ball applies to the floor, which causes the ball to bounce.

• The floor applies a larger amount of force to the ball than the ball applies to the floor, which causes the ball to bounce.

• The floor applies a larger amount of force to the ball than the ball applies to the floor because it is a part of the Earth.

• The ball applies a larger amount of force to the floor than the floor applies to the ball because the ball bounces.

Astronomers recently discovered that galaxies are accelerating away from each other. What can astronomers infer from this observation?

• Galaxies must be moving along circular paths.

• Galaxies will begin to slow down again in the near future.

• There must be an unbalanced force acting on galaxies in the universe.

• There must not be any forces acting on galaxies, otherwise they would slow down.

Sami wants to build the fastest racing bike possible. What is one way he can change the bike, so she has a better chance of winning the race?

• reduce the mass of the bike so it accelerates more quickly

• put on smoother tires to eliminate friction with the race track

• increase the mass of the bike to increase its gravitational field

• replace metal parts with plastic to decreases its magnetic field

A table of position vs. time data for an object is shown below. Which of the following could be a possible force diagram for the object whose motion is described in the data table?

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• 
• 
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Which statement describes a situation where the acceleration is zero?

• Only objects at rest experience an acceleration of zero.

• Only objects moving at a constant speed in a positive direction experience an acceleration of zero.

• Both objects at rest and objects moving at constant velocity experience an acceleration of zero.

• Only objects moving at a constant speed in a negative direction experience an acceleration of zero.

Which of the following is a correct example of an interacting force pair as described by Newton’s third law?

• A hammer applies a force on the nail it strikes, and the nail exerts an equal amount of force on the hammer.

• Earth pulls down on the chair, and the ground pushes up on the chair with an equal amount of force.

• A car drives down the road at a constant velocity, and the driver applies a force to the brake to stop the car.

• A skydiver reaches constant velocity when the force of air resistance equals the force of gravity.

A force of 3750 N acts on the truck in a direction opposite to its motion. According to the graph, what is the mass of the truck?

• 10 kg

• 16 kg

• 1000 kg

• 1500 kg

Which of the following must be true if an object is accelerating?

• It must be slowing down.

• It must be speeding up.

• At least one unbalanced, external force must be acting on it.

• Balanced forces are causing it to change its velocity.