Microquiz_1 - MicroQuiz 2.1 Does the displacement of an...

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Unformatted text preview: MicroQuiz 2.1 Does the displacement of an object depend on the specific location of the origin of the coordinate system? Displacement 1) yes 2) no 3) it depends on the coordinate system MicroQuiz 2.1 A Does the displacement of an object depend on the specific location of the origin of the coordinate system? Displacement 1) yes 2) no 3) it depends on the coordinate system Since the displacement is the difference between two coordinates, the origin does not matter. 10 20 30 40 50 30 40 50 60 70 MicroQuiz 2.2 Does the odometer in a car measure distance or displacement? Odometer 1) distance 2) displacement 3) both MicroQuiz 2.2 A Does the odometer in a car measure distance or displacement? Odometer 1) distance 2) displacement 3) both If you go on a long trip and then return home, your odometer does not measure zero, but it records the total miles that you traveled. That means the odometer records distance. Follow-up: How would you measure displacement in your car? MicroQuiz 2.3 Does the speedometer in a car measure velocity or speed? Speedometer 1) velocity 2) speed 3) both 4) neither MicroQuiz 2.3 A Does the speedometer in a car measure velocity or speed? Speedometer 1) velocity 2) speed 3) both 4) neither The speedometer clearly measures speed, not velocity. Velocity is a vector (depends on direction), but the speedometer does not care what direction you are traveling. It only measures the magnitude of the velocity, which is the speed. Follow-up: How would you measure velocity in your car? MicroQuiz 2.4 Velocity in One Dimension 1) yes 2) no 3) it depends If the average velocity is non-zero over some time interval, does this mean that the instantaneous velocity is never zero during the same interval? MicroQuiz 2.4 A Velocity in One Dimension 1) yes 2) no 3) it depends If the average velocity is non-zero over some time interval, does this mean that the instantaneous velocity is never zero during the same interval? No!!! For example, your average velocity for a trip home might be 60 mph, but if you stopped for lunch on the way home, there was an interval when your instantaneous velocity was zero, in fact! MicroQuiz 2.5 When throwing a ball straight up, which of the following is true about its velocity v and its acceleration a at the highest point in its path? Acceleration II 1) both v = 0 and a = 0 2) v 0, but a = 0 3) v = 0, but a 0 4) both v 0 and a 0 5) not really sure MicroQuiz 2.5 A When throwing a ball straight up, which of the following is true about its velocity v and its acceleration a at the highest point in its path? Acceleration II 1) both v = 0 and a = 0 2) v 0, but a = 0 3) v = 0, but a 0 4) both v 0 and a 0 5) not really sure At the top, clearly v = 0 because the ball has momentarily stopped. But the velocity of the ball is changing, so its acceleration is definitely not zero! Otherwise it would remain at rest!! Follow-up: ...and the value of a is...? y MicroQuiz 2.6 You throw a ball straight up into the air. After it leaves your hand, at what point in its flight does it have the maximum value of acceleration? Free Fall I 1) its acceleration is constant everywhere 2) at the top of its trajectory 3) halfway to the top of its trajectory 4) just after it leaves your hand 5) just before it returns to your hand on the way down MicroQuiz 2.6 A You throw a ball straight up into the air. After it leaves your hand, at what point in its flight does it have the maximum value of acceleration? Free Fall I 1) its acceleration is constant everywhere 2) at the top of its trajectory 3) halfway to the top of its trajectory 4) just after it leaves your hand 5) just before it returns to your hand on the way down The ball is in free fall once it is released. Therefore, it is entirely under the influence of gravity, and the only acceleration it experiences is g, which is constant at all points. MicroQuiz 2.7 Alice and Bill are at the top of a building. Alice throws her ball downward. Bill simply drops his ball. Which ball has the greater acceleration just after release? Free Fall II 1) Alice's ball 2) it depends on how hard the ball was thrown 3) neither -- they both have the same acceleration 4) Bill's ball Alice v0 vA Bill vB MicroQuiz 2.7 A Alice and Bill are at the top of a building. Alice throws her ball downward. Bill simply drops his ball. Which ball has the greater acceleration just after release? Both balls are in free fall once they are released, therefore they both feel the acceleration due to gravity (g). This acceleration is independent of the initial velocity of the ball. Free Fall II 1) Alice's ball 2) it depends on how hard the ball was thrown 3) neither -- they both have the same acceleration 4) Bill's ball Alice v0 vA Bill vB Follow-up: Which one has the greater velocity when they hit the ground? MicroQuiz 2.8 Up in the Air 1) vA < vB 2) vA = vB 3) vA > vB 4) impossible to tell Alice and Bill are at the top of a cliff of height H. Both throw a ball with initial speed v0, Alice straight down and Bill straight up. The speeds of the balls when they hit the ground are vA and vB. If there is no air resistance, which is true? Alice v0 v0 vA vB Bill H MicroQuiz 2.8 A Up in the Air 1) vA < vB 2) vA = vB 3) vA > vB 4) impossible to tell Alice and Bill are at the top of a cliff of height H. Both throw a ball with initial speed v0, Alice straight down and Bill straight up. The speeds of the balls when they hit the ground are vA and vB. If there is no air resistance, which is true? Bill's ball goes up and comes back down to Bill's level. At that point, it is moving downward with v0, the same as Alice's ball. Thus, it will hit the ball ground with the same speed as Alice's ball. Alice v0 v0 vA vB Bill H Follow-up: What happens if there is air resistance? MicroQuiz 2.9 You drop a rock off a bridge. When the rock has fallen 4 m, you drop a second rock. As the two rocks continue to fall, what happens to their separation? Throwing Rocks 1) the separation increases as they fall 2) the separation stays constant at 4 m 3) the separation decreases as they fall 4) it is impossible to answer without more information MicroQuiz 2.9 A You drop a rock off a bridge. When the rock has fallen 4 m, you drop a second rock. As the two rocks continue to fall, what happens to their separation? Throwing Rocks 1) the separation increases as they fall 2) the separation stays constant at 4 m 3) the separation decreases as they fall 4) it is impossible to answer without more information At any given time, the first rock always has a greater velocity than the second rock, therefore it will always be increasing its lead as it falls. Thus, the separation will increase. MicroQuiz 2.10 The graph of position versus time for a car is given below. What can you say about the velocity of the car over time? Graphing Velocity 1) it speeds up all the time 2) it slows down all the time 3) it moves at constant velocity 4) sometimes it speeds up and sometimes it slows down 5) not really sure x t MicroQuiz 2.10 A The graph of position versus time for a car is given below. What can you say about the velocity of the car over time? Graphing Velocity 1) it speeds up all the time 2) it slows down all the time 3) it moves at constant velocity 4) sometimes it speeds up and sometimes it slows down 5) not really sure x The car moves at a constant velocity because the x vs. t plot shows a straight line. The slope of a straight line is constant. Remember that the slope of x versus t is the velocity! t v MicroQuiz 2.11 t v Rubber Balls I t 1 v 3 v t 2 You drop a rubber ball. Right after it leaves your hand and before it hits the floor, which of the above plots represents the v vs. t graph for this motion? (Assume your y-axis is pointing up). t 4 v MicroQuiz 2.11 A t v Rubber Balls I t 1 v 3 v t 2 You drop a rubber ball. Right after it leaves your hand and before it hits the floor, which of the above plots represents the v vs. t graph for this motion? (Assume your y-axis is pointing up). t 4 The ball is dropped from rest, so its initial velocity is zero. Since the yzero axis is pointing upward and the ball is falling downward, its velocity is negative and becomes more and more negative as it accelerates downward. v MicroQuiz 2.12 t v Rubber Balls II 1 v 3 t v 2 You toss a ball straight up in the air and catch it again. Right after it leaves your hand and before you catch it, which of the above plots represents the v vs. t graph for this motion? (Assume your y-axis is pointing up). t 4 t v MicroQuiz 2.12 A Rubber Balls II v t 1 v 3 t v 2 You toss a ball straight up in the air and catch it again. Right after it leaves your hand and before you catch it, which of the above plots represents the v vs. t graph for this motion? (Assume your y-axis is pointing up). t 4 t The ball has an initial velocity that is positive but diminishing as it slows. It stops at the top (v = 0), and then its velocity becomes negative and becomes more and more negative as it accelerates downward. v MicroQuiz 2.13 t v v Rubber Balls III 1 2 3 t v t t 4 You drop a very bouncy rubber ball. It falls, and then it hits the floor and bounces right back up to you. Which of the following represents the v vs. t graph for this motion? v MicroQuiz 2.13 A t v v Rubber Balls III 1 2 3 t v t t 4 You drop a very bouncy rubber ball. It falls, and then it hits the floor and bounces right back up to you. Which of the following represents the v vs. t graph for this motion? Initially, the ball is falling down, so its velocity must be negative (if UP is positive). Its velocity is also increasing in magnitude as it falls. Once it bounces, it changes direction and then has a positive velocity, which is also decreasing as the ball moves upward. ...
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This note was uploaded on 05/13/2010 for the course PHYSICS 53L taught by Professor Mueller during the Fall '07 term at Duke.

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