Newton's laws review

Which of the following does NOT describe one of Newton’s Laws of Motion?

• All objects will remain in their current state of motion unless acted upon by an unbalanced force.

• All forces in the universe occur in equal but oppositely directed pairs.

• Objects will remain in motion even when unbalanced forces are applied.

• The acceleration of an object is directly proportional to the net force acting on it and indirectly proportional to its mass.

Answer explanation

The statement 'Objects will remain in motion even when unbalanced forces are applied' is incorrect. According to Newton's laws, unbalanced forces change an object's state of motion.

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NGSS.HS-PS2-1

A stone that is being pushed forward with a force of 20 N and encounters a surface frictional force of 5 N. What is the net force acting on the stone?

• 20 N forward

• 5N backward

• 25N forward

• 15N forward

Answer explanation

The net force is calculated by subtracting the frictional force from the applied force: 20 N (forward) - 5 N (backward) = 15 N forward. Thus, the correct answer is 15 N forward.

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NGSS.MS-PS2-2

A 25 kg object is given a net force of 500 N. What is its acceleration?

• 10 m/s²

• 20 m/s²

• 2 m/s²

• 250 m/s²

Answer explanation

Using Newton's second law, F = ma, we can find acceleration (a) by rearranging the formula to a = F/m. Here, a = 500 N / 25 kg = 20 m/s². Thus, the correct answer is 20 m/s².

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NGSS.MS-PS2-2

Which of these statements about forces is always true?

• Objects will accelerate when a balanced force is applied.

• A force results only when two objects contact each other.

• An action force is always equal and opposite to a reaction force.

• A force is necessary to continue an object’s motion.

Answer explanation

The statement 'An action force is always equal and opposite to a reaction force' is true according to Newton's Third Law of Motion, which states that for every action, there is an equal and opposite reaction.

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NGSS.MS-PS2-2

A rock has two forces acting on it, 50 N to the left and 34 N to the right. If the box has a mass of 4 kg, what is its acceleration?

• 2.1 m/s² to the left

• 21 m/s² to the left

• 0.4 m/s² to the left

• 4m/s² to the left

Answer explanation

The net force is 50 N (left) - 34 N (right) = 16 N (left). Using F = ma, acceleration a = F/m = 16 N / 4 kg = 4 m/s² to the left. Thus, the correct answer is 4 m/s² to the left.

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NGSS.MS-PS2-2

Alex holds a baseball weighing 1.4 N at rest on the palm of his hand. What is the net force acting on the baseball?

• 1.4 N

• 0.14 N

• 0 N

• 14 N

Answer explanation

The baseball is at rest, meaning the forces acting on it are balanced. The weight of the baseball (1.4 N) is countered by the upward force from Alex's hand, resulting in a net force of 0 N.

Tags

NGSS.MS-PS2-2

According to Newton’s 2nd Law of Motion (F = ma), increasing the mass of an object will cause the acceleration to _____________

• Increase

• Decrease

• Stay the same

Answer explanation

According to Newton's 2nd Law (F = ma), if the force (F) is constant and the mass (m) increases, the acceleration (a) must decrease to maintain the equation. Thus, increasing mass results in decreased acceleration.

Tags

NGSS.MS-PS2-2

A box is being pushed up a ramp. Which way is the friction force acting?

• Up the ramp, parallel to the ramp

• Down the ramp, parallel to the ramp

• Perpendicular to the ramp

• Straight down

Answer explanation

The friction force opposes the motion of the box. Since the box is being pushed up the ramp, friction acts down the ramp, parallel to it, resisting the upward movement.

An airplane is flying in a straight line, at a constant elevation (height), with a decreasing velocity. Which statement correctly describes lift, weight, thrust, and drag forces acting on the plane? Hint: on a scratch sheet of paper draw an FBD for the plane.

• Thrust is less than drag; lift and weight are equal

• All four forces on the plane are equal

• Thrust and drag are equal; lift is greater than weight

• Thrust is greater than drag; lift and weight are equal

Answer explanation

As the airplane is flying at a constant elevation with decreasing velocity, thrust must be less than drag to cause deceleration. Lift equals weight to maintain altitude, confirming the correct choice: thrust is less than drag; lift and weight are equal.

Tags

NGSS.MS-PS2-2

A satellite with a mass of 100 kg collides with a meteor with a force of 700 N. If the meteor is traveling at a constant velocity after the collision, what is its acceleration?

• 7000 m/s²

• 0 m/s²

• 700 m/s²

• 7 m/s²

Answer explanation

The meteor is traveling at a constant velocity after the collision, which means its acceleration is 0 m/s². Acceleration is defined as the change in velocity over time, and constant velocity implies no change.

Tags

NGSS.MS-PS2-2

NGSS.MS-PS2-1