Homework 2 Sol.

Homework 2 Sol. - Abd Elhai, Mohamed Homework 2 Due: Feb 4...

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Abd Elhai, Mohamed – Homework 2 – Due: Feb 4 2008, 11:00 pm – Inst: Dr Kevin Dean 1 This print-out should have 33 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 2 It is due by 09:00 Abu Dhabi time on Tuesday morning, 5 January(23:00 Monday in Texas) 001 (part 1 o± 5) 1 points Consider the displacement curve: OABC 0 1 2 - 2 - 1 0 1 2 x (m) t (s) Displacement vs Time O A B C Choose the appropriate quantity ±or the average velocity v OA ±rom point O to A . 1. v OA = +2 m/s correct 2. v OA = + 3 m/s 3. v OA = - 2 m/s 4. v OA = 0 m/s 5. v OA = - 3 m/s Explanation: Defnitions: Average velocity: v = displacement time Average speed: s = distance time Instantaneous velocity: v = d x dt Instantaneous speed: s = | v | Solution: Note that the displacement x is on the ver- tical axis and that time t is on the horizontal axis. The key here is to know that velocity uses net displacement in its equation while speed uses total distance traveled. v OA = x A - x O t A - t O = 2 - 0 1 - 0 = +2 m / s . The values ±or the average velocity come di- rectly ±rom evaluating the defnitions. 002 (part 2 o± 5) 1 points Choose the appropriate quantity ±or the aver- age velocity v OB ±or the motion ±rom point O to point B . 1. v OB = + 3 m/s 2. v OB = +2 m/s 3. v OB = 0 m/s correct 4. v OB = - 3 m/s 5. v OB = - 2 m/s Explanation: v OB = x B - x O t B - t O = 0 - 0 2 - 0 = 0 m / s . 003 (part 3 o± 5) 1 points Choose the appropriate quantity ±or the aver- age speed s OB ±or the motion ±rom point O to point B . 1. s OB = 0 m/s 2. s OB = +2 m/s correct 3. s OB = + 3 m/s 4. s OB = - 2 m/s

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Abd Elhai, Mohamed – Homework 2 – Due: Feb 4 2008, 11:00 pm – Inst: Dr Kevin Dean 2 5. s OB = - 3 m/s Explanation: s OB = | x A - x O | + | x B - x A | t B - t O = 2 + 2 2 - 0 = +2 m / s . The values for the average speed come directly from evaluating the de±nitions. 004 (part 4 of 5) 1 points Choose the appropriate quantity for the in- stantaneous velocity v B at point B . 1. v B = - 2 m/s correct 2. v B = +2 m/s 3. v B = 0 m/s 4. v B = + 3 m/s 5. v B = - 3 m/s Explanation: The instantaneous velocity at point B can be obtained by ±rst ±nding an expression for the graph describing the position of the mov- ing object and taking its derivative evaluated at time t B . However, since the graph near B is linear, it is simpler to calculate the slope of the line over the interval from A to B . The result correctly describes the instantaneous velocity at B because the derivative of a straight line is constant at all points on the line and can be obtained for our case by v B = x B - x A t B - t A = 0 - 2 2 - 1 = - 2 m / s . 005
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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 2 Sol. - Abd Elhai, Mohamed Homework 2 Due: Feb 4...

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