PHY12345.docx - Copyright 1997 1998 Richard Hochstim All...

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10 km x Copyright ç 1997, 1998 Richard Hochstim. All rights reserved. Terms of use. [email protected] Translational Motion Thanks for downloading THE MCAT EXCELERATOR™. Although they are only rough drafts, I hope these chapters will help you out on the MCAT. I’d love to hear any comments, corrections or suggestions you may have. Rich — [email protected] « The chapters on physics which follow, require some quantitaive skills that were introduced in the preceding chapter. «In the text below, s is used to represent distance, and d is used represent displacement. In college physics texts, the use of these symbols has not been standardized. 1.1 Basic Concepts Speed «Average speed is a scalar quantity. It is defined as distance, s, over the change in time, ∆t . assignment » A car travels 10 km north for 30 minutes, than 10 km east for 15 minutes, then 10 km south for 15 minutes. What is the average speed of the car over the entire trip in km/hr? solution: 10 km 10 km distan ce 10 km The total distance traveled is 30 km. Dividing by the total elapsed time of 1.0 hr, gives an average speed of 30 km/hr. Displacement «Displacement , d , is a vector quantity that represents change in position. It is graphically depicted by an arrow with its tail on the initial position, , and its head on the final position, x . 10 km 10 km distan ce Average speed = s d = x distance
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10 km Velocity «Average velocity , v , is a vector quantity. It is defined as the displacement, over the change in time. displacement
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2 » T HE M CAT E XCELERATOR v = lim d ∆t0 ∆t v = d ∆t assignment » For the previous example what is the average velocity over the course of the trip in km/hr? solution: The displacement is 10 km due east. Dividing by the total elapsed time of 1.0 hr, gives, an average velocity of 10 km/hr due east. Instantaneous Velocity « Instantaneous velocity is a vector quantity. As t approaches zero, t h e average velocity becomes the instananeous velocity. When an objects position is plotted against time, the slope of the curve at any given instant in time, is the instantaneous velocity. Acceleration « Acceleration , a , is a vector quantity. It is defined as the change in velocity, over the change i n time. A change in either the magnitude or the direction of the velocity is an acceleration. Uniform acceleration occurs when the change in velocity with respect to time is a constant. Zero Acceleration When the velocity remains constant there is no acceleration. The graphs below depict this situation. Time Time Tim e Note that the slope of the graph on the left is equal to the velocity. Since this is a linear plot, the velocity remains constant over time, as depicted in the central graph. Since the velocity is constant, the acceleration is zero.
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