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Unformatted text preview: Web Assign Ch2 HW3 f10 (Homework) Ashlyn Baum Physics 303K, section B, Fall 2010 Instructor: Jim Chelikowsky Current Score : 26.5 / 27.5 Due : Wednesday, September 8, 2010 11:30 PM CDT 1. 2/2 points Question: MI3 2.6.X.050 (a) A runner starts from rest and in 2 s reaches a speed of 6 m/s. If we assume that the speed changed at a constant rate (constant net force), what was the average speed during this 2 s interval? average speed = 3 3 m/s (b) How far did the runner go in this 2 s interval? distance = 6 6 m (c) The driver of a car traveling at a speed of 22 m/s slams on the brakes and comes to a stop in 4 s. If we assume that the speed changed at a constant rate (constant net force), what was the average speed during this 4 s interval? average speed = 11 11 m/s (d) How far did the car go in this 4 s interval? distance = 44 44 m Solution or Explanation If the rate of change of the velocity is constant (constant net force, constant acceleration), the average velocity is the arithmetic mean of the initial and final velocities. 2. 2/2 points Question: MI3 2.6.X.051 (c) Why does the formula used in part (b) give the wrong answer? The due date for this assignment is past. Your work can be viewed below, but no changes can be made. On a straight road with the + x axis chosen to point in the direction of motion, you drive for 3 hours at a constant 20 miles per hour, then in a few seconds you speed up to 80 miles per hour and drive at this speed for 1 hour. (a) What was the x component of average velocity for the 4hour period, using the fundamental definition of average velocity, which is the displacement divided by the time interval? v avg, x = 35 35 miles per hour (b) Suppose instead you use the formula v avg, x = . What do you calculate for the x component of average velocity? v avg, x = = 50 50 miles per hour v ix + v fx 2 v ix + v fx 2 Page 1 of 7 Ch2 HW3 f10 11/21/2010 http:[email protected][email protected].. Solution or Explanation If the rate of change of the velocity is constant (constant net force, constant acceleration), the average velocity is the arithmetic mean of the initial and final velocities. But this is not a case of constant acceleration, so we cannot calculate the average velocity from the arithmetic mean....
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This note was uploaded on 11/21/2010 for the course PHY 56665 taught by Professor Chelikowsky during the Fall '10 term at University of Texas.
 Fall '10
 Chelikowsky

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