301 (F97) Exam #1 Solution

301 (F97) Exam #1 Solution -...

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Unformatted text preview: 7########,################y##]#######_#######{####################h####h##5 ####5####5####M#.##############(##A####]#(#######P###x##{###M# ##m####'#*##Q###5#############m######### ## #=##'####'####'####'####'####'####Name #1. [35 points] Block A is resting on top of block B as shown in the diagram at right. The mass of block B is twice that of block A. A. [20 pts] The blocks are moving to the right on a table at constant speed, and block A does not slip relative to block B.# i. In the space provided, draw a separate free-body diagram for each block. Explicitly label the forces as instructed in class. Draw your vectors roughly to scale. ii. If both members of any third law (action/reaction) force pairs appear in the free-body diagrams above, identify them with tick marks as was done in class.#B. [15 pts] While the blocks are moving to the right, a hand pushes horizontally on block B as shown in the diagram at right. Block A does not slip relative to block B.i. What is the direction of the acceleration of block B? Explain your reasoning. Block B is moving in a straight line and slowing down. The change in velocity over a short time interval, and thus the acceleration, is opposite the velocity. Thus the acceleration of block B is to the left. ii. How would the magnitudes of the forces exerted now on block A differ, if at all, with those indentified above in Part A? Explain your reasoning. iii. How does the magnitude of the net force on block A compare to the magnitude of the net force on block B? If the net force on either block is zero, state that explicitly. Explain your reasoning. Since block A does not slip relative to block B, the two blocks move as a unit and have the same velocity and the same acceleration. Using Newtons second law, #o(F,) = #o(F,)net = m#o(a,), since the blocks have the same acceleration, the block with the larger mass has the larger net force. Thus, block B has the larger net force. #2. [35 pts total] Block U is on top of an identical block L. A person pushes horizontally on block U as shown. NOTE: There is no friction between the table and the blocks, however, there is sufficient friction between the blocks that they do not slide relative to one another. A. [6 pts] Draw a free-body diagram for the lower block L. Draw and label the forces as in class to make clear: the object exerting the force the object on which the force acts the type of force (normal, frictional, gravitational, etc.)B. [6 pts] Draw a free-body diagram for the upper block U. Label the forces as above.#C. [6 pts] If both members of any third law force pairs appear in the diagrams for parts A and B, identify both members of each pair....
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This document was uploaded on 10/29/2011 for the course PHSX 301 at MSU Bozeman.

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301 (F97) Exam #1 Solution -...

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