Question

3. Two blocks are tied together with a rope R of mass M. Block B is pushed to the right with a constant horizontal force Fa. Assume that there is no friction, and that the blocks and the rope are already in motion when we start our observations. For simplicity, let's ignore the a) Describe in general terms the motion of the two blocks connected by the rope Rope has mass M FB Note: In lecture we introduced tension in ropes by assuming that the ropes themselves are "massless" and that the effects of ropes can be "ignored" when applying Newton's laws of motion. If a rope has real mass (such as rope R in this situation) then we need to take its mass into account when applying Newton's laws of motion. In other words, the rope will have its own free-body diagram (FBD) and at least some of the applied force must go into moving the rope as well as the blocks. b) Draw a free body diagram for each block and the rope connecting them. For simplicity, let's ignore the vertical forces and concentrate on the horizontal forces only. Block A Rope Block B c) Identify al the Newton's third-law force pairs on your diagrams by placing an X, XX, etc. on each member of the pair Analysis tip: when identifying action-reaction pairs it helps to label forces with subscripts indicating both the object exerting the force and the object that "receives that force. For example, the tension (or "action" force) of the rope on object A could be labeled FRin object A's FBD to indicate the force exerted by the rope R on object A Then, there should be a corresponding "reaction" force on the rope's FBD labeled FA-R

Answer 1

(a) So in the given situation when block 'B' will be given a push then block B will move forward and in sometime a tension will be generated in the rope. This tension will exert a force on block A which will result into forward motion of A. (b) FBD of B (only considering the horizontal forces) FBD of (only considering horizontal forces) FBD of rope (only considering horizontal forces) c) The mutual forces belonging to Newton's third law of motion here is only 'tension'.