WQ6.1 12/13 points (graded) Three identical bricks are pushed across a table at constant speed. The hand pushes horizontally. There is also friction between the bricks and the table. a) On a piece of paper draw separate free-body diagrams for system A and system B. Label each of the forces in your diagrams. If the forces are part of an action/reaction pair use the following notation FA on B to show that system A exerts a force of system B. Enter 'yes' below once you've completed your diagrams. yes Answer: 'yes' or Your diagrams should look like the following: A B FA A on B Finan There are only two forces on B, friction holding it back and the force FA on B from A pushing it forward. Since it is not accelerating we know these forces have equal magnitude. For system A, since it is twice as massive, we know the frition force will be twice the magnitude of the friction force on B. Also, the action/reaction pair of forces between A and B implies that FB on A is equal magnitude to FA on B. Since system A is not accelerating we know that the remaining force, coming from the hand, must have magnitude equal to the sum of F Bon A and F friction. This means that all together Fhand has a magnitude equal to three times the friction force on system B. b) Compare the magnitude of the net force on system A (two bricks) to that on system B (one brick) Énet,A = Înet,B OFnet,A > É net,B OFnet,A < Înet,B V
c) Explain your answer for b): the same Answer: 'the same' or no net force or zero force or zero acceleration for both or constant speed or constant velocity or constant or zero The net force on each block is zero! This is because the blocks are not accelerating so there must be zero net force. d) The magnitude of the force exerted on system A by system Bis the magnitude of the force exerted on system B by system A. greater than less than equal to > e) Explain your answer for d): newton's third law V Answer: action/reaction pair or The forces form an action/rection pair so their magnitudes must be equal. f) Would your answer change if the hand were pushing system B to the left instead of pushing system A to the right? yes no V g) Explain your answer for f): newton's third law V Answer: action/reaction pair or Again, the forces form an action/rection pair so their magnitudes must be equal.
g) Rank the magnitudes of all the horizontal forces (which should have all been identified on your free-body diagram.)? O Fhand > Ffriction, A = Ffriction, B = FBon A = FA on B Fhand > Ffriction, A > Ffriction, B = FB on A = FAon B O Fhand = Ffriction, A = Ffriction, B = FB on A = FA on B O Fhand