Chapter 2 Solutions


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CHAPTER 2 KINEMATICS IN ONE DIMENSION ANSWERS TO FOCUS ON CONCEPTS QUESTIONS 1. (b) Displacement, being a vector, conveys information about magnitude and direction. Distance conveys no information about direction and, hence, is not a vector. 3. (c) The average speed is the distance of 16.0 km divided by the elapsed time of 2.0 h. The average velocity is the displacement of 0 km divided by the elapsed time. The displacement is 0 km, because the jogger begins and ends at the same place. 6. (c) The average acceleration is the change in velocity (final velocity minus initial velocity) divided by the elapsed time. The change in velocity has a magnitude of 15.0 km/h. Since the change in velocity points due east, the direction of the average acceleration is also due east. 10. (c) The equations of kinematics can be used only when the acceleration remains constant and cannot be used when it changes from moment to moment. 13. (d) According to one of the equation of kinematics ( ) 2 1 00 2 , with 0 m/s xv t a t v =+ = , the displacement is proportional to the acceleration. 19. (b) Free-fall is the motion that occurs while the acceleration is solely the acceleration due to gravity. While the rocket is picking up speed in the upward direction, the acceleration is not just due to gravity, but is due to the combined effect of gravity and the engines. In fact, the effect of the engines is greater than the effect of gravity. Only when the engines shut down does the free-fall motion begin. 24. (a) The slope of the line in a position versus time graph gives the velocity of the motion. The slope for part A is positive. For part B the slope is negative. For part C the slope is positive.
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Chapter 2 Problems 45 CHAPTER 2 KINEMATICS IN ONE DIMENSION PROBLEMS ______________________________________________________________________________ 8. REASONING The younger (and faster) runner should start the race after the older runner, the delay being the difference between the time required for the older runner to complete the race and that for the younger runner. The time for each runner to complete the race is equal to the distance of the race divided by the average speed of that runner (see Equation 2.1). SOLUTION The difference between the times for the two runners to complete the race is , where 50 18 tt () 50 18 50-yr-old 18-yr-old Distance Distance and Average Speed Average Speed == (2.1) The difference between these two times (which is how much later the younger runner should start) is 50 18 50-yr-old 18-yr-old 33 Distance Distance Average Speed Average Speed 10.0 10 m 64 s 4.27 m/s 4.39 m/s −= ×× =−= ______________________________________________________________________________ 12. REASONING The definition of average velocity is given by Equation 2.2 as Average velocity = Displacement/(Elapsed time). The displacement in this expression is the total displacement, which is the sum of the displacements for each part of the trip.
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This note was uploaded on 12/20/2010 for the course PHYSICS 203 taught by Professor Croft during the Spring '08 term at Rutgers.

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