Homework 4 Sol.

# Homework 4 Sol. - Abd Elhai Mohamed Homework 4 Due 11:00 pm...

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Abd Elhai, Mohamed – Homework 4 – Due: Feb 18 2008, 11:00 pm – Inst: Dr Kevin Dean 1 This print-out should have 19 questions. Multiple-choice questions may continue on the next column or page – fnd all choices be±ore answering. The due time is Central time. This is ONLINE HOMEWORK No 4 It is due 09:00 Tuesday morning, 19 Febru- ary (Abu Dhabi time) - (same as 23:00 Mon- day night in Texas). 001 (part 1 o± 3) 5 points You are driving a car down a straight road at a constant 51 miles per hour. Consider the ±ollowing ±orces: I) air drag pushing back on the car; II) gravity pulling down on the car; III) the ground pushing up on the car; IV) ±riction pushing the wheels (and the car) ±orward; and V) ±riction pushing the wheels (and the car) back. Which ±orce(s) act on the car? 1. I, II, III and IV correct 2. II, III and IV 3. I and II 4. I, III and V 5. I, II and III Explanation: There are ±our ±orces acting on the car. The ground pushing up on the car balances the gravity pushing down in the vertical di- rection; the ±riction between the wheels and the ground pushing the car ±orward balances the air drag pushing back on the car. 002 (part 2 o± 3) 5 points Is there a net or unbalanced ±orce acting on the car? 1. No; the speed is constant. 2. Yes; a net ±orce in the horizontal direc- tion. 3. Cannot be determined 4. No; the velocity is constant. correct 5. Yes; a net ±orce in the vertical direction. Explanation: According to Newton’s frst law, a moving object will continue moving in a straight line at a constant speed until acted upon by an unbalanced ±orce. The car’s speed is constant and its direction does not change, so there is no net ±orce acting on the car. 003 (part 3 o± 3) 5 points A±ter a while, the car started to go around a long bend, still maintaining its constant speed o± 55 miles per hour. Is there a net (unbalanced) ±orce acting on the car? 1. No; the velocity o± the car does not change. 2. Cannot be determined 3. Yes; its direction is not the same as the velocity. correct 4. Yes; its direction is the same as the veloc- ity. 5. No; the speed o± the car does not change. Explanation: The direction o± the net ±orce is the same as the direction o± acceleration, which is directed inward (toward the center o± the curve). keywords: 004 (part 1 o± 3) 5 points A 5 kg object is subjected to two ±orces, ~ F 1 = (1 . 9 N) ˆ ı + ( - 2 . 7 N) ˆ and ~ F 2 = (4 . 2 N) ˆ ı + ( - 11 . 5 N) ˆ . The object is at rest at the origin at time t = 0. What is the magnitude o± the object’s ac- celeration? Correct answer: 3 . 09095 m / s 2 . Explanation:

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Abd Elhai, Mohamed – Homework 4 – Due: Feb 18 2008, 11:00 pm – Inst: Dr Kevin Dean 2 Let : ~ F 1 = (1 . 9 N) ˆ ı + ( - 2 . 7 N) ˆ , ~ F 2 = (4 . 2 N) ˆ ı + ( - 11 . 5 N) ˆ , and ~v o = 0 m / s . ~ F
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## This note was uploaded on 02/16/2010 for the course PHYSICS 191262 taught by Professor Najafzadeh during the Spring '09 term at The Petroleum Institute.

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Homework 4 Sol. - Abd Elhai Mohamed Homework 4 Due 11:00 pm...

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