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# h2_6a - Homework Assignment 2 Solutions Displacement vs...

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Homework Assignment 2 Solutions Displacement vs. Time Graphs The motions described in each of the questions take place at an intersection on a two-lane road with a stop sign in each direction. For each motion, select the correct position versus time graph. For all of the motions, the stop sign is at the position x=0, and east is the positive x direction. A) A driver ignores the stop sign and continues driving east at constant speed. Answer: D B) A driver ignores the stop sign and continues driving west at constant speed. Answer: A C) A driver, traveling west, slows and stops at the stop sign. Answer: F D) A driver, after stopping at the stop sign, accelerates to the east. Answer: E

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Displacement vs. Time Graphs The figure below shows the position of a moving object as a function of time. A) Find the average velocity of this object from points A to B, B to C, and A to C. Answer: v AB , v BC ,v AC = 3.00,1.50,1.80 m / s B) For the intervals in Part A, would the average speed be less than, equal to, or greater than the values you found in that Part? Answer: equal
Velocity from Graphs of Position versus Time An object moves along the x axis during four separate trials. Graphs of position versus time for each trial are shown in the figure. A) During which trial or trials is the object's velocity not constant? Answer: Trial B The graph of the motion during Trail B has a changing slope and therefore is not constant. The other trials all have graphs with constant slope and thus correspond to motion with constant velocity. B) During which trial or trials does the object have the greatest average velocity? Answer: Trial B You recognized that although the magnitudes of the average velocity in Trial B and Trial D are equal, their directions are opposite. This makes the average velocity in Trial D less than the average velocity in Trial B. The object does not move during Trial C, so it has an average velocity of zero. During Trial A the object has a positive average velocity but its magnitude is less than that in Trial B.

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The Graph of a Sports Car's Velocity The graph in the figure shows the velocity v of a sports car as a function of time t. Use the graph to answer the following questions. A) Find the maximum velocity v max of the car during the ten-second interval depicted in the graph. Answer: v max = 55 m / s B) During which time interval is the acceleration positive? Answer: t = 0 s to t = 4 s C) Find the maximum acceleration a max of the car. Answer: a max = 30 m / s 2 D) Find the minimum magnitude of the acceleration a min of the car. Answer: a min = 0 m / s 2 E) Find the distance d 0,2 traveled by the car between t =0 s and t = 2 s. Answer: d = 55 m
Problem 2.6 A little cat, Bella, walks in a straight line, which we shall call the x axis, with the positive direction to the right. As an observant scientist, you make measurements of her motion and construct a graph of the little feline's velocity as a function of time.

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