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phys1111 ch2 solutions

# phys1111 ch2 solutions - CHAPTER 2 KINEMATICS IN ONE...

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CHAPTER 2 KINEMATICS IN ONE DIMENSION CONCEPTUAL QUESTIONS ____________________________________________________________________________________________ 1. REASONING AND SOLUTION The displacement of the honeybee for the trip is not the same as the distance traveled by the honeybee. As stated in the question, the distance traveled by the honeybee is 2 km. The displacement for the trip is the shortest distance between the initial and final positions of the honeybee. Since the honeybee returns to the hive, its initial position and final position are the same; therefore, the displacement of the honeybee is zero. ____________________________________________________________________________________________ 2. REASONING AND SOLUTION The buses do not have equal velocities. Velocity is a vector, with both magnitude and direction. In order for two vectors to be equal, they must have the same magnitude and the same direction. The direction of the velocity of each bus points in the direction of motion of the bus. Thus, the directions of the velocities of the buses are different. Therefore, the velocities are not equal, even though the speeds are the same. ____________________________________________________________________________________________ 3. REASONING AND SOLUTION The average speed of a vehicle is defined as the total distance covered by the vehicle divided by the time required for the vehicle to cover the distance. Both distance and time are scalar quantities. Since the average speed is the ratio of two scalar quantities, it is a scalar quantity. ____________________________________________________________________________________________ 4. SSM REASONING AND SOLUTION Consider the four traffic lights 1 , 2 , 3 and 4 shown below. Let the distance between lights 1 and 2 be x 12 , the distance between lights 2 and 3 be x 23 , and the distance between lights 3 and 4 be x 34 . v x 12 x 34 x 23 1 2 3 4 The lights can be timed so that if a car travels with a constant speed v , red lights can be avoided in the following way. Suppose that at time t = 0 s, light 1 turns green while the rest are red. Light 2 must then turn green in a time t 12 , where t 12 = x 12 / v . Light 3 must turn green in a time t 23 after light 2 turns green, where t 23 = x 23 / v . Likewise, light 4 must turn

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45 KINEMATICS IN ONE DIMENSION green in a time t 34 after light 3 turns green, where t 34 = x 34 / v . Note that the timing of traffic lights is more complicated than indicated here when groups of cars are stopped at light 1. Then the acceleration of the cars, the reaction time of the drivers, and other factors must be considered. ____________________________________________________________________________________________ 5. REASONING AND SOLUTION The velocity of the car is a vector quantity with both magnitude and direction The speed of the car is a scalar quantity and has nothing to do with direction. It is possible for a car to drive around a track at constant speed. As the car drives around the track, however, the car must change direction. Therefore, the direction of the velocity changes , and the velocity cannot be constant. The incorrect statement is (a). ____________________________________________________________________________________________ 6. REASONING AND SOLUTION Answers will vary. One example is a ball that is thrown straight up in the air. When the ball is at its highest point, its velocity is momentarily zero.
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phys1111 ch2 solutions - CHAPTER 2 KINEMATICS IN ONE...

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