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qz3sol_6942s11 - a What is the acceleration of the block Is...

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TA: Tomoyuki Nakayama Monday, February 14, 2011 PHY 2048: Physic 1, Discussion Section 6942 Quiz 3 (Homework Set #5) Name: UFID: Formula sheets are not allowed. Do not store equations in your calculator. You have to solve problems on your own; memorizing final algebraic expressions from homework assignments and just plugging numbers into them will not give you full credit. Leave all your work. ________________________________________________________________________________ In the figure below right, a 50.0-kg block lies on the floor of a 850 kg elevator cab that is being pulled upward by a cable through distance d = 2.50 m. The normal force on the block from the floor has constant magnitude F N = 450 N.
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Unformatted text preview: a) What is the acceleration of the block? Is it speeding up or slowing down? Two forces are exerted on the block: the normal force from the floor and the gravitational force. Taking upward as positive, we apply Newton’s 2 nd to the block. ma = F N – mg ⇒ a = (F N – mg)/m = -0.800 m/s Since the elevator is moving upward, the negative acceleration means it is slowing down. b) How much work is done on the cab by the force from the cable? Three forces are exerted on the elevator: the tension force, the gravitational force and downward force F N from the block. Newton’s 2 nd law yields Ma = T – Mg - F N T = M(g+a) + F N = 8100 N The work done by the tension is W T = Td = 20250 J...
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qz3sol_6942s11 - a What is the acceleration of the block Is...

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