Forces and Blocks, Part I

Newton's 2nd & 3rd Laws

I. Constant Velocity
Three identical bricks are pushed across a table at constant speed as shown. The arrow pushes horizontally. (Note: there is friction between the bricks and the table.)

 

Call the stack of two bricks System A and the single brick, System B.

A. How does the magnitude of the force exerted on System A by System B compare to the magnitude of the force exerted on System B by System A? ("Compare" in this case means indicate whether equal, larger, or smaller.) Explain.

Would your answer change if the arrow were pushing System B to the left instead of pushing System A to the right? If so, how? If not, why not?

 

B. For the case that the arrow pushes on System A, draw separate free-body diagrams for each of the systems A and B. Label each of the forces in your diagrams by identifying: a) the type of force, b) the object on which the force is exerted, and c) the object exerting the force.


C. Rank the magnitudes of all the horizontal forces that you identified above in order from largest to smallest. (Recall that the bricks are pushed so that they move at constant speed.)