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course Phy 231
2-3-11 about 12:00am
The problem:A ball starts with velocity 0 and accelerates uniformly down a ramp of length 30 cm, covering the distance in 5 seconds.
• What is its average velocity?
answer/question/discussion (start in the next line):
30cm/5sec= 6cm/sec
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• If the acceleration of the ball is uniform then its average velocity is equal to the average of its initial and final velocities.
You know its average velocity, and you know the initial velocity is zero.
What therefore must be the final velocity?
answer/question/discussion (start in the next line):
(v_f – 0)/2= 6cm/sec, v_f= 6cm/sec * 2= 12cm/sec= v_f
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• By how much did its velocity therefore change?
answer/question/discussion (start in the next line):
12cm/sec
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• At what average rate did its velocity change with respect to clock time?
answer/question/discussion (start in the next line):
(12cm/sec – 0)/(5sec – 0)= 2.4cm/sec/sec
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• What would a graph of its velocity vs. clock time look like? Give the best description you can.
answer/question/discussion (start in the next line):
A straight line with endpoints (0,0) and (5,12). The slope would be 2.4
@& The points would be (0 sec, 0 cm/s) and (5 sec, 12 cm/s), the rise would be 12 cm/s, the run would be 5 sec, and the slope would be 2.4 (cm/s/)s = 2.4 cm/s^2 or 2.4 cm/s/s.
The units are essential at every step (as you did in preceding calculations), and give meaning to the slope of this graph.*@
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&#Good responses. See my notes and let me know if you have questions. &#