If you're seeing this message, it means we're having trouble loading external resources on our website.

If you're behind a web filter, please make sure that the domains *.kastatic.org and *.kasandbox.org are unblocked.

To log in and use all the features of Khan Academy, please enable JavaScript in your browser.

Main content

Course: AP®︎/College Physics 1 > Unit 2

Lesson 2: Newton's third law and free body-diagrams

© 2024 Khan AcademyTerms of use Privacy Policy Cookie Notice

Newton's third law and free-body diagrams

Google Classroom

Two boxes of equal mass are pulled along a rough floor by the force F shown in the figure below. The boxes have a resulting acceleration of

2.5 {m/s}^{2}

to the right.

Which of the following statements correctly compares the forces box A and B exert on one another?

(Choice A)
The force exerted on box B by box A is larger because it must be added to the applied force F.
(Choice B)
The boxes exert the same size force on one another, because this is an action-reaction pair.
(Choice C)
The force exerted on box A by box B is smaller because box B is pulling only half the mass of the system.
(Choice D)
The force exerted on box A by box B is smaller because there is only one force acting on box A.

Related content

Video 13 minutes 6 seconds

More on Newton's third law

Video 8 minutes

Newton's third law of motion