Final answer:
The correct free-body diagram for block B should show a frictional force to the left equal in magnitude to the horizontal component of the force pulling the two blocks to ensure their constant velocity.
Step-by-step explanation:
The question poses a scenario where two blocks, A and B, are being pulled to the right along a horizontal surface by a 100-N force and are moving at a constant velocity. Since the blocks are moving at a constant velocity, we can deduce that the net horizontal force on each block is zero.
This means that the frictional force acting on the lower block, B, must be equal and opposite to the horizontal component of the pull to ensure the block's constant velocity. Without seeing the figures in question, we can state generally that the correct free-body diagram for block B would show a frictional force to the left which is equal in magnitude to the part of the 100-N force that is effectively pulling block B to the right.
For answering questions regarding a block sliding on a surface or being pulled, you must consider the gravitational force, normal force, frictional force, and any applied forces. When the question mentions constant velocity, Newton's first law tells us that the forces must be balanced. The coefficient of friction can also help determine the magnitude of frictional force using the formula μ×normal force. However, since we do not have the actual figures to examine, we can only provide this theoretical guidance.