8.6c

Safety belts protect people in cars in the event of an accident because, according to Newton’s Laws of Motion, when an impact causes the car to suddenly change its motion, -

• the people in the car will continue to move in the same direction and at the same speed as before the impact.

• the speed of the car always increases, giving it greater force since the mass will remain the same.

• the speed of the people always increases, since now they have, not one, but two forces acting on them.

• the car now has a greater overall mass - its own mass plus the mass of the object by which it has been struck.

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A ball thrown into the air starts out with an initial upward velocity, but eventually slows and stops before falling back to the ground. Which of the following contributes the most to the change in motion of the ball?

• The initial force with which the ball is thrown

• The downward force of gravity

• The resistance against the atmosphere

• The increase of inertia

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• 1st
• 2nd
• 3rd

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The tendency of an object to resist changes in its motion is...

• inertia

• force

• acceleration

• velocity

The combination of all the forces acting on an object is the...

• net force

• action force

• reaction force

• balance force

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The masses of four vehicles and the net forces acting on them as they enter a highway are recorded in the table below. Which vehicle has the greatest acceleration as it enters the highway?

• Sedan

• Coupe

• SUV

• Truck

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The force that opposes motion between two surfaces in contact with each other.

• inertia

• friction

• momentum

• gravity

A force that opposes motion between a surface in contact with the atmosphere.

• air resistance

• gravity

• momentum

• terminal velocity

Use Newton's first law of motion to explain why the car stopped when it hit the book.

• Book= balanced force/ Car= change in motion

• Book= balanced force/ Car= constant motion

• Book= unbalanced force/ Car= change in motion

• Book= unbalanced force/ Car= constant motion

The penny on the car represents a passenger in vehicle. How would a seat belt change the motion of a passenger in a collision?

• seat belt= unbalanced force that continues the passenger's motion

• seat belt= unbalanced force that stops the passenger from continuing motion through windshield

• seat belt= balanced force that continues the passenger's motion

• seat belt= balanced force that stops the passenger from continuing motion through windshield

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