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 force diagram of the horizontal forces exerted on the lower block,B?
E)None of these diagrams is correct.

Question

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 force diagram of the horizontal forces exerted on the lower block,B?
E)None of these diagrams is correct.

Quizplus · Accepted Answer

According to Newton's 2nd law, the force exerted on an object is equal to its mass multiplied by its acceleration. Since both blocks are moving with a constant velocity, their acceleration is zero. Therefore, the net force acting on each block must be zero as well. The force diagram for block B should show a 100 N force to the right (from the pull), and an equal and opposite 100 N force to the left (from the friction with block A). Option B shows this correctly. Option A does not show the leftward force, Option C shows an unbalanced force to the right, and Option D shows an unbalanced force with no friction between the two blocks. Therefore, the correct answer is B.

Two Blocks,A and B,are Being Pulled to the Right Along