Exam1_2011_Winter_Solutions

Exam1_2011_Winter_Solutions - Physics 140, Winter 2011...

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Physics 140, Winter 2011 First Midterm Exam Physics Department, University of Michigan February 3, 2011 FORM 1 Please print your name: ____SAUL LOU SHEN______________ Your INSTRUCTOR:_________________________ INSTRUCTIONS AND INFORMATION 1. Fill in YOUR NAME, INSTRUCTOR and the EXAM FORM NUMBER on the scantron. 2. RECORD YOUR ANSWERS ON THE SCANTRON USING A #2 PENCIL. 3. Turn in this exam copy with your scantron answer sheet. 4. This is a 90-minute, closed book exam. You may use one 3” x 5” card on which you have your favorite equations. You also may use a calculator but please do not share calculators. 5. All cell phones and other communication devices must be shut off and out of sight. 6. There are altogether 20 multiple choice questions. All questions are of equal value. Equations/values that you may find useful: s f = s i + v 0 t + ½ a t 2 v f = v 0 + at a rad = v 2 /r F = m a F k = μ k N g = 9.8 m/s 2
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Physics 140, Winter 2011, Midterm 1 Problem 1: The value of is: A. zero B. +1 C. –1 D. 3 E. Answer C. Problem 2: Figure shows a 10 kg mass suspended from two spring scales, each of which has negligible weight. Thus, A. Each scale will read 5 kg. B. The top scale will read zero, the lower scale will read 10 kg. C. The lower scale will read zero, the top scale will read 10 kg. D. Each scale will read between 1 kg and 10 kg, such that the two add to 10 kg. E. None of the above. Each scale will measure the tension (divided by g ). The tension is 10 g in both. Answer E. Problem 3: A child standing on a bridge throws a rock straight down. The rock leaves the child’s hand at t = 0. Which of the graphs best represents the velocity of the stone as a function of time? Neglect air resistance. 10kg 0 A v y t 0 B v y t 0 C v y t 0 D v y t 0 E v y t
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If we take up positive then . The initial velocity is down so it’s negative too. A line with a negative intercept and a slope of – g . Answer C. Problem 4: Three boxes with mass m 1 = 1kg, m 2 = 2kg, and m 3 = 3kg are hanging from strings as shown in figure. You are pulling the top string with the force of 100N. What is the tension T 12 in the string connecting boxes m 1 and m 2 ? A. 20 N B. 49 N C. 59 N D. 72 N E. 83 N Treating all three objects together and just grouping 2 and 3 give the following FBDs: Calling up positive Newton’s 2 nd Law gives for all three and for the bottom two. Solve for a in the first equation and plug into the 2 nd equation: N. Answer E. Problem 5: 100 N m 1 =1kg m 2 =2 kg m 3 =3 kg (1+2+3) g T 12 m 2 =2 kg m 3 =3 kg (2+3) g T 23 T 12 100 N m 1 =1kg m 2 =2 kg m 3 =3 kg
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A small remote-control car with mass 1.60 kg moves at a constant speed of 12.0 m/s in a vertical circle inside a hollow metal cylinder that has a radius of 5.00 m. What is the magnitude of the normal force exerted on the car by the walls of the cylinder at the top of the vertical circle? A.
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This note was uploaded on 02/15/2012 for the course PHYS 140 taught by Professor Uher during the Winter '10 term at University of Michigan.

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Exam1_2011_Winter_Solutions - Physics 140, Winter 2011...

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