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PHY131_F04_M1_Solutions - MIDTERM SET A Physics 131 Fall'04...

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MIDTERM SET A Physics 131 Page 1 October 4, 2004 Physics 131, Fall ’04 Midterm Examination (Set A) October 4 th , 2004 Instructions & Guide-lines to Students & Proctors: 1) Write your name and SBU ID number on each blue book you use 2) Solve any three of the four problems 3) Start a new problem solution a new page Miscellaneous: You can use the formula sheet (ONE A4 page) you brought with you You can use any calculator GOOD LUCK! Problem 1: (10 points) Ms. Missed Opportunity (MO) who missed a class on friction in Physics 131 is traveling in a large freight elevator in the year 2054. She has a box containing computer equipment with mass 100 kg sitting at the farthest possible position with respect to the elevator door and wants to move closer to the door. The coefficient of friction between the box and the elevator floor, μ static , is 0.1. Ms. MO can control the acceleration “a” of the elevator either upward or downward. You are visiting SBU to celebrate your 50 th Physics 131 Class Reunion and just happen to be in the elevator! a) What advise would you give Ms. MO regarding the direction she should set the acceleration “a” (upward or downward) to make her life easy? Write down explicitly the equations for frictional forces involved in this problem under the two conditions to convince Ms. Missed Opportunity of your advice. b) The magnitude of acceleration “a” can be set to 0.5g (where g is the acceleration due to gravity) upward or downward. Ms. MO is capable of exerting no more than 50N horizontal force by herself. Will she be able to move the box to the door after taking your advice? Problem 2: (10 points) City A lies directly west of City B. When there is no wind Captain Dare A. Devil (licensed to fly in the State of Florida during September 2004) makes a round trip of 6000 km between the two in 10 hrs in his airplane, while traveling at same speed up and down. Once a strong steady wind was
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MIDTERM SET A Physics 131 Page 2 October 4, 2004 blowing from west to east, and the round trip took him 12 hrs. How fast was the wind blowing? Problem 3: (10 points) At a certain part of your drive from home to school your car (mass m) coasts along in neutral at a constant speed v if there is no wind (ignore drag forces in this problem). Examination of topographical map shows that for this stretch of straight highway, the elevation decreases by an amount h for every segment of road length L traveled by your car. If the g is the acceleration due to gravity: a) What is the total resistive force that needs to be overcome for the car to travel with constant velocity v? Express your answer in terms of elevation h and road length segment L.
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