Assignment 04 Solutions, P2207 F11

# Assignment 04 Solutions, P2207 F11 - Name Physics 2207 Fall...

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Name: __________________________________ Physics 2207, Fall 2011, Assignment 4 Solutions Cornell University 1 Physics 2207, Fall 2011, Assignment 4 Solutions 1. Chapter 5 Problem 15. In this problem we will treat the spring scale and cords as “massless”. The mass of the salami is kg 0 . 11 m . (a) Apply Newton’s 2 nd law to the salami along the vertical ( y ) direction: 0 cord sal, Earth sal, cord sal, y ma mg F F F . N 108 ) m/s 81 . 9 )( kg 0 . 11 ( 2 cord sal, mg F . Apply Newton’s 2 nd law to the spring scale along the vertical ( y ) direction: 0 below cord scale, above cord scale, F F . below cord scale, above cord scale, F F . By Newton’s 3 rd law: N 108 cord sal, sal cord, mg F F and below cord scale, scale below, cord F F . The “cord below” is the same cord that’s connected to the salami. Since this cord is not accelerating, by Newton’s 2 nd law (free-body diagram for this cord is not shown), 0 sal cord, scale below, cord F F . So, N 108 sal cord, scale below, cord mg F F . Again, by Newton’s 3 rd law, N 108 below cord scale, scale below, cord mg F F , and from Newton’s 2 nd law applied to the spring scale (see above) N 108 below cord scale, above cord scale, mg F F . Thus, the two cords connected to the spring scale both pull on it with forces each of magnitude 108 N, and so the spring scale reads 108 N. (b) Again, by arguments similar to those in Part (a), the scale reads 108 N. Earth sal, F cord sal, F below cord scale, F above cord scale, F x y Earth sal, F cord sal, F right cord scale, F left cord scale, F

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Physics 2207, Fall 2011, Assignment 4 Solutions Cornell University 2 1. (Continued.) (c) Again, the spring scale reads 108 N. 2. Chapter 5 Problem 24. kg 0 . 2 m . i ˆ ) N 20 ( 1 F . Since the box only accelerates along the x direction, the second horizontal force 2 F can only have an x component. Apply Newton’s 2 nd law to the box along the x direction: x x ma F F , 2 1 . 1 , 2 F ma F x x . (a) 0 i ˆ ) N 20 ) m/s 10 )( kg 0 . 2 (( i ˆ ) ( 2 1 2 F ma F x .
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Assignment 04 Solutions, P2207 F11 - Name Physics 2207 Fall...

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