8.6C Formative Assessment

You are riding in a vehicle with a coffee cup on the dashboard while traveling 30km/h. The vehicle makes a sudden stop to avoid hitting the car that has stopped in front of it.

Which illustration best demonstrates what would happen to the coffee cup?

• It will go forward.

• It will go backward.

• It will stay stationary.

• It will go straight up.

A magician performs a trick where the tablecloth is quickly removed from the table, while all of the items on the table stay in the same place. Which statement below accurately describes the reason that the items remain on the table?

• The mass of the items on the table is so small that no force was applied when the tablecloth was pulled out from under the items.

• The direction of the force applied to the tablecloth was down towards the ground, so the items accelerated down towards the table until they rested on the table.

• The action force of the moving tablecloth caused a reaction force from the items on the table, so the forces in the items remained balanced and the items remained at rest on the table.

• The moving tablecloth did not apply much force to the items, so the forces on the items remained mostly balanced allowing the items to remain at rest on the table.

During a demonstration of Newton's laws of motion, a student used the setup shown in the image below. The student flicked the index card with a fingertip, and the coin fell straight down into a plastic cup as shown.

Which of these best explains why the coin fell straight down into the cup instead of remaining on the index card?

• The coin was at rest until the card was removed, so it tended to remain in the same location. Once the card was gone, the unbalanced force of gravity caused the coin to fall.

• Moving the card applied an action force on the coin. Since the card was gone, gravity applied a reaction force on the coin.

• The card had less mass than the coin, so a smaller force of gravity acted on the card. The lager force of gravity on the coin made it fall.

• The acceleration of the coin falling into the cup was equal and opposite to the acceleration of the card.

A student jumps off a sled toward the west after it stops at the bottom of an icy hill.

Based on the law of action- reaction, in what direction will the sled most likely move as the student jumps off?

• North

• South

• East

• West

The risk of injury in a car accident is much greater if occupants do not wear a seat belt. Which of Newton's Laws explains why this is true? In 3-5 complete sentences, explain your answer.

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