# PS4 - Physics16 Spring2010 ProblemSet4 5 . 62 . IDENTIF Y:...

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Physics 16 ʹ Spring 2010 ʹ Problem Set 4 5 . 62 . IDENTIFY: Apply m ¦ F= a & & to each object . Constant speed means 0 . SET UP: The free-body diagrams are sketched in Figure 5.62. 1 T is the tension in the lower chain, 2 is the tension in the upper chain and F is the tension in the rope. E XECUTE: The tension in the lower chain balances the weight and so is equal to w . The lower pulley must have no net force on it, so twice the tension in the rope must be equal to and the tension in the rope, which equals , is 2 . Then, the downward force on the upper pulley due to the rope is also , and so the upper chain exerts a force on the upper pulley, and the tension in the upper chain is also . E VALUATE: The pulley combination allows the worker to lift a weight by applying a force of only /2 . Figur e 5 . 62

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5 . 65 . IDENTIFY: Apply m ¦ F= a & & to each block. SET UP: Constant speed means 0 . When the blocks are moving, the friction force is k f and when they are at rest, the friction force is s . E XECUTE: (a) The tension in the cord must be 2 mg in order that the hanging block move at constant speed. This tension must overcome friction and the component of the gravitational force along the incline, so ± ² 21 1 sin cos k ȝPJ DD ³ and (sin cos ) ȝ ³ . (b) In this case, the friction force acts in the same direction as the tension on the block of mass 1 , so k 1 (s i n c o s ) ĮȝP J Į ´ , or k ĮF R V ± ȝ D ´ . ( c ) Similar to the analysis of parts (a) and (b), the largest 2 could be is 1s DP D ³ and the smallest 2 could be is ´ . E VALUATE: In parts (a) and (b) the friction force changes direction when the direction of the motion of 1 changes. In part (c), for the largest 2 the static friction force on 1 is directed down the incline and for the smallest 2 the static friction force on 1 is directed up the incline. 5 . 66 . 7KH V\VWHP LV LQ HTXLOLEULXP± \$SSO\ 1HZWRQ¶V ²VW ODZ WR EORFN A , to the hanging weight and to the knot where the cords meet. Target variables are the two forces.

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## This note was uploaded on 04/15/2010 for the course PHYSICS 16 taught by Professor N.darnton during the Spring '10 term at Smith.

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PS4 - Physics16 Spring2010 ProblemSet4 5 . 62 . IDENTIF Y:...

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