Unit 8.1 Quiz 5

How would the amount of force on the head compare to the amount of force on the object it collides with in each system A, B, and C?

• In every collision, the peak force on the head would be different than the peak force on the other object in the collision.

• In some, but not all, collisions the peak force on the head would be the same as the peak force on the other object in the collision.

• In every collision, the peak force on the head would be the same as the peak force on the other object in the collision.

Answer explanation

In every collision, according to Newton's third law, the forces exerted by the head and the other object are equal in magnitude and opposite in direction. Therefore, the peak force on the head would be the same as the peak force on the other object.

Tags

NGSS.MS-PS2-2

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In the previous question, you were asked, "How would the amount of force on the head compare to the amount of force on the object it collides with in each system A, B, and C?"

Explain your answer to that question.

• The forces would only be equal in system B, because the two objects in the collision are the same.

• The force on the ground in system C would be greater than the force on the head because the grass is soft and not moving, but the force on the head in System A and B would be equal to the force of the other object in the collision because in both systems the objects are moving.

• In each scenario, the forces on the head would be equal to the force on the object it collides with because forces come in equal and opposite pairs.

• Since the objects in the collision with the head are all different, the force and the head would be different than the force on the other objects.

Answer explanation

In each scenario, the forces on the head are equal to the forces on the colliding object due to Newton's third law, which states that for every action, there is an equal and opposite reaction.

Tags

NGSS.MS-PS2-2

NGSS.MS-PS2-1

Considering both objects that are about to collide in each interaction, which system would have the least amount of kinetic energy in the system right before a collision? Assume that player #84 is moving at 7 m/s.

• Player #84 running and heading the soccer ball that was kicked by another player.

• Player #84 running and colliding with another running player running towards them.

• Player #84 running and hitting the ground.

• All the situations have the same amount of kinetic energy.

Answer explanation

Player #84 running and hitting the ground has the least kinetic energy because only their own mass and speed contribute, unlike the other scenarios where additional mass and speed from other players or the ball increase the total kinetic energy.

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NGSS.MS-PS2-2

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NGSS.MS-PS3-5

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In the previous question you were asked which system would have the least amount of kinetic energy right before a collision.

Explain your answer to the previous question:

• The player is not moving as fast as the ball.

• The players can’t run that fast.

• The ground is not moving.

• The amount of kinetic energy is always the same.

Answer explanation

The ground is not moving, so it has no kinetic energy. In contrast, the player and the ball are in motion, which means they possess kinetic energy. Therefore, the ground has the least amount of kinetic energy before the collision.

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Force is needed:

• to prevent a moving object from turning.

• for a motionless object to remain still.

• for a moving object to keep moving at the same speed and direction.

• for a moving object to change its speed.

Answer explanation

Force is required to change the speed of a moving object, as per Newton's second law. The other options do not accurately describe the role of force in motion.

Tags

NGSS.MS-PS2-2

A fan cart is moving forward on a frictionless surface. If you change the fan speed from High to Low, what will occur?

• The cart will keep moving at the same speed.

• The cart will slow down.

• The cart will stop moving.

• The cart will continue to speed up, but not as quickly as before.

Answer explanation

When the fan speed is reduced from High to Low, the thrust decreases, but the cart will still continue to speed up due to its momentum, just not as quickly as before.

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NGSS.MS-PS2-2

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The speed-versus-time bar graph for a fan cart experiment is shown. What could have happened?

• The track was frictionless, and the fan was changed from High to Low after 8 seconds.

• The track was frictionless, and the fan was changed from High to Off after 8 seconds.

• The track was wooden, and the fan was changed from High to Off after 8 seconds.

• The track was wooden, and the fan was changed from Off to Low after 8 seconds.

Answer explanation

The correct choice indicates a frictionless track where the fan was switched from High to Off after 8 seconds, resulting in a decrease in speed. This aligns with the graph showing a drop in speed at that time.

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NGSS.MS-PS3-1

What causes objects to change their motion?

• a net force

• an equal and opposite force

• potential energy

• kinetic energy

Answer explanation

A net force is required to change an object's motion, as stated in Newton's second law. It is the unbalanced force that causes acceleration, while equal and opposite forces cancel each other out.

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NGSS.MS-PS2-2

NGSS.MS-PS2-1

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