8.6C Applying Newton's Laws of Force and Motion

1. Which is Newton's Third Law?

• Force = mass x acceleration

• The amount of acceleration depends on the size of the net force and the mass of the object.

• For every action there is an equal and opposite reaction.

• Objects at rest or in motion will stay at rest or in motion unless an external force acts upon that object.

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The amount of force colliding objects impose on one another depends on what?

• Their mass

• Their velocity

• Their weight

• It doesn't depend on anything. They will always impose the same amount of force on one another.

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NGSS.MS-PS2-1

A man is trying to pull an elephant off of the road but it doesn't move. The man pulls on the rope with a force of 5000 N. How much force does the elephant pull on the rope?

• None, the elephant isn't moving so it isn't exerting any forces.

• The answer is unknown unless we know the mass of the elephant.

• 2,500 N

• 5,000 N

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NGSS.MS-PS2-1

A small car runs into a parked truck, which is much bigger than the car. Which of the following statements is correct?

• The force that the car exerts on the truck is bigger than the force the truck exerts on the car because the car is moving and the truck is not.

• The force that the car exerts on the truck is smaller than the force the truck exerts on the car because the car has a smaller mass.

• The force that the car exerts on the truck is equal to the force the truck exerts on the car.

• The car exerts a force on the truck, but the truck does not exert a force on the car because it is not moving. Only moving objects can exert forces.

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NGSS.MS-PS2-1

Carlos is pulling his little brother on a sled at a constant speed. He is exerting a force of 128 N on the sled. Together, his brother and the sled have a mass of 32 kg. What is the acceleration of the sled?

Hint: Net Force = Mass x Acceleration; be sure to rearrange the equation to solve for ACCELERATION

• 96 m/s²

• 4096 m/s²

• 4 m/s²

• 0.25 m/s²

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NGSS.MS-PS2-2

The Law of Inertia says that objects resist changes in motion due to their inertia. What is responsible for keeping an object at rest or maintaining an object's constant velocity?

• External Forces

• Unbalanced Forces

• Gravity

• Balanced Forces

• Friction

According to Newton's first law of motion, what would happen to a car traveling west at a constant velocity of 55 MPH in the absence of an unbalanced force?

• The car would continue moving west with a velocity of 55 MPH.

• The car would slowing increase its velocity approaching but not reaching the speed of light.

• The car would slow down but never reach 0 velocity.

• The car would slow down and come to a stop.

• The car would increase its velocity without changing acceleration.

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Jasmine is trying to hang a new clock in her apartment. The clock experiences a force due to the gravity of 15N. She has a nail that exerts an upward force of 10N. Are the forces on her clock balanced or unbalanced and what will happen to the clock?

• The forces are unbalanced and the clock will fall.

• The forces are balanced, but the clock will still fall.

• The forces are unbalanced and the clock will fly upward.

• The forces are balanced and the clock will stay on the wall.

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NGSS.MS-PS2-2

1. In physics class, a box slides across the table with an applied force of 20N. The students measure the net force to be 14N. What must the frictional force acting on the block be?

Hint: Friction opposes motion.

• 6 N

• 34 N

• 14 N

• 20 N

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NGSS.MS-PS2-1

1. In physics class, students roll a toy car across the table. The toy car has a mass of 3kg. The students apply a force of 10 N to the car and friction holds it back with 1 N of force. What is the acceleration of the car?

Hint: FIRST calculate the Net Force, THEN use a = F/m to calculate acceleration.

• 3 m/s²

• 3.67 m/s²

• 7 m/s²

• 6 m/s²

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