Two Blocks, a and B, Are Being Pulled to the Right

Multiple Choice

Two blocks, A and B, are being pulled to the right along a horizontal surface by a horizontal 100-N pull, as shown in the figure. Both of them are moving together at a constant velocity of 2.0 m/s to the right, and both weigh the same. Which of the figures below shows a correct free-body diagram of the horizontal forces acting on the lower block, B?

A)

B)

C)

D)

E) None of these diagrams is correct.