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21_Physics ProblemsTechnical Physics

21_Physics ProblemsTechnical Physics - 22 Motion in One...

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22 Motion in One Dimension Q2.8 Yes. If you drop a doughnut from rest v = 0 a f , then its acceleration is not zero. A common misconception is that immediately after the doughnut is released, both the velocity and acceleration are zero. If the acceleration were zero, then the velocity would not change, leaving the doughnut floating at rest in mid-air. Q2.9 No: Car A might have greater acceleration than B, but they might both have zero acceleration, or otherwise equal accelerations; or the driver of B might have tramped hard on the gas pedal in the recent past. Q2.10 Yes. Consider throwing a ball straight up. As the ball goes up, its velocity is upward v > 0 a f , and its acceleration is directed down a < 0 a f . A graph of v vs. t for this situation would look like the figure to the right. The acceleration is the slope of a v vs. t graph, and is always negative in this case, even when the velocity is positive. v t v 0 FIG. Q2.10 Q2.11 (a) Accelerating East (b) Braking East (c) Cruising East (d) Braking West (e) Accelerating West (f) Cruising West (g)
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