Newton's third law Knowledge-Based Practice

Questions

1. 1.

   A passenger stands on the floor of an elevator that is accelerating upward. According to Newton's third law, how does the magnitude of the upward contact force exerted by the floor on the passenger compare to the downward contact force exerted by the passenger on the floor?

   • A) They are equal in magnitude at all times, regardless of the elevator's acceleration.
   • B) The force exerted by the floor is greater in magnitude because the passenger is accelerating upward.
   • C) The force exerted by the passenger is greater in magnitude because their weight adds to the downward force.
   • D) The force exerted by the floor is greater in magnitude during acceleration, but they become equal at constant speed.
2. 2.

   Which of the following pairs of forces represents an action-reaction pair according to Newton's third law?

   • A) The downward gravitational pull on a resting box and the upward normal force exerted on the box by the floor
   • B) The backward force exerted by a car's tires on the road and the forward force exerted by the road on the tires
   • C) The forward thrust provided by an airplane's engine and the backward air resistance acting on the airplane
   • D) The upward tension force exerted by a cable on an elevator and the downward gravitational force acting on the elevator
3. 3.

   Two ice skaters stand at rest facing each other on frictionless ice. If Skater X exerts a horizontal force of 50 N to the right on Skater Y, what force does Skater Y exert on Skater X according to Newton's third law?

   • A) 0 N, because Skater Y remains passive and does not actively push back
   • B) 25 N to the left, because the applied force is split equally between both skaters
   • C) 50 N to the left, directly opposite to the force exerted by Skater X
   • D) 50 N to the right, pushing in the same direction as Skater X
4. 4.

   A worker pulls horizontally on a rope attached to a heavy crate, causing it to slide across a rough floor. According to Newton's third law, what is the reaction force to the horizontal pull exerted by the rope on the crate?

   • A) The backward frictional force exerted by the floor on the crate
   • B) The downward gravitational force exerted by Earth on the crate
   • C) The forward pulling force exerted by the worker on the rope
   • D) The backward pulling force exerted by the crate on the rope
5. 5.

   According to Newton's third law, which statement correctly describes a universal property of every action-reaction force pair?

   • A) The two forces act on the same object to maintain mechanical equilibrium.
   • B) The two forces are always of the same physical type and occur simultaneously.
   • C) The action force occurs first and produces the reaction force with a brief time delay.
   • D) The forces can only exist when the interacting objects are in direct physical contact.
6. 6.

   How does a rocket engine produce forward acceleration in the vacuum of space according to Newton's third law?

   • A) It pushes against the surrounding ambient particles remaining in space.
   • B) It creates a forward-facing vacuum that pulls the rocket forward.
   • C) It releases high-temperature exhaust that eliminates all backward forces on the hull.
   • D) It exerts a backward force on the expelled exhaust gases, which exert an equal and opposite force forward on the rocket.
7. 7.

   According to Newton's third law, when a sprinter pushes backward against the track with their spikes, which force directly accelerates the sprinter forward?

   • A) The downward gravitational force exerted by Earth on the sprinter
   • B) The internal muscular force exerted by the sprinter's leg muscles
   • C) The backward contact force exerted by the sprinter's spikes on the track
   • D) The forward contact force exerted by the track on the sprinter's spikes
8. 8.

   Why do the two forces in a Newton's third law action-reaction pair never cancel each other out?

   • A) They act on two different objects rather than on a single object.
   • B) They act sequentially one after the other rather than simultaneously.
   • C) They have unequal magnitudes whenever an object accelerates.
   • D) They act in perpendicular directions rather than along the same line.
9. 9.

   A physics textbook rests stationary on a flat horizontal table. According to Newton's third law, what is the reaction force to the downward gravitational force that Earth exerts on the textbook?

   • A) The upward normal force exerted by the table on the textbook
   • B) The downward contact force exerted by the textbook on the table
   • C) The upward normal force exerted by Earth on the table
   • D) The upward gravitational force exerted by the textbook on Earth
10. 10.

    A massive truck collides head-on with a lightweight car. How does the magnitude of the force exerted by the truck on the car compare to the magnitude of the force exerted by the car on the truck during the collision?

    • A) The truck exerts a greater force because it has significantly more mass and momentum.
    • B) The two forces are equal in magnitude because they constitute an action-reaction pair.
    • C) The car exerts a greater force because it experiences a much larger acceleration during the collision.
    • D) The truck exerts a greater force only if its speed immediately before the impact was greater than the car's speed.

Answers and step-by-step solutions appear after you finish the test.