course Phy 231
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20:25:24 Physics video clip 01: A ball rolls down a straight inclined ramp. It is the velocity the ball constant? Is the velocity increasing? Is the velocity decreasing?
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RESPONSE --> When a ball rolls down a straight inclined ramp, the velocity of the ball increases at a constant rate.
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20:36:12 ** It appears obvious, from common experience and from direct observation, that the velocity of the ball increases. A graph of position vs. clock time would be increasing, indicating that the ball is moving forward. Since the velocity increases the position increases at an increasing rate, so the graph increases at an increasing rate. **
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RESPONSE --> ok
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20:38:35 If the ball had a speedometer we could tell. What could we measure to determine whether the velocity of the ball is increase or decreasing?
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RESPONSE --> To determine whether the whether the velocity of the ball in increasing, we could compare the time it takes the ball to travel down one half of the ramp to the time it takes to travel down the entire ramp.
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20:40:38 What is the shape of the velocity vs. clock time graph for the motion of the ball?
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20:43:34 ** If the ramp has an increasing slope, the velocity would increase at an increasing rate and the graph would curve upward, increasing at an increasing rate. If the ramp has a decreasing slope, like a hill that gradually levels off, the graph would be increasing but at a decreasing rate. On a straight incline it turns out that the graph would be linear, increasing at a constant rate, though you aren't expected to know this at this point. All of these answers assume an absence of significant frictional forces such as air resistance. **
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20:48:22 A ball rolls down ramp which curves upward at the starting end and otherwise rests on a level table. What is the shape of the velocity vs. clock time graph for the motion of the ball?
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RESPONSE --> The graph of velocity of a ball on this ramp will increase at a decreasing rate, gradually levelling off. It will be concave down. Since our real life ball will encounter frictional forces, the graph will eventually begin to decrease if the ramp were long enough.
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20:48:44 ** While on the curved end the ball will be speeding up, and the graph will therefore rise. By the time the ball gets to the level part the velocity will no longer be increasing and the graph will level off; because of friction the graph will actually decrease a bit, along a straight line. As long as the ball is on the ramp the graph will continue on this line until it reaches zero, indicating that the ball eventually stops. In the ideal frictionless situation on an infinite ramp the line just remains level forever. **
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20:50:15 For the ball on the straight incline, we would certainly agree that the ball's velocity is increasing. Is the velocity increasing at a constant, an increasing, or a decreasing rate? What does the graph of velocity vs. clock time look like?
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RESPONSE --> The ball on a straight incline has a velocity that increases at a constant rate. The graph of velocity vs. time is linear and increasing.
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20:51:18 ** It turns out that on a straight incline the velocity increases at a constant rate, so the graph is a straight line which increases from left to right. Note for future reference that a ball on a constant incline will tend to have a straight-line v vs. t graph; if the ball was on a curved ramp its velocity vs. clock time graph would not be straight, but would deviate from straightness depending on the nature of the curvature (e.g., slope decreasing at increasing rate implies v vs. t graph increasing at increasing rate).**
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???}??V???`?????assignment #001 ???F?X???}??_??Physics I 06-09-2006
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21:40:37 Briefly state what you think velocity is and how you think it is an example of a rate.
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RESPONSE --> Velocityis how we measure how fast an object is moving. It is the rate of change in an object's position with respect to time.
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21:41:30 ** A rate is a change in something divided by a change in something else. This question concerns velocity, which is the rate of change of position: change in position divided by change in clock time. **
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21:43:08 Given average speed and time interval how do you find distance moved?
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RESPONSE --> Multiplying average speed by a time interval results in the distance moved.
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21:43:12 ** You multiply average speed * time interval to find distance moved. For example, 50 miles / hour * 3 hours = 150 miles. **
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21:46:28 Given average speed and distance moved how do you find the corresponding time interval?
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RESPONSE --> Dividing the distance by the speed results in the time interval.
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21:46:44 ** time interval = distance / average speed. For example if we travel 100 miles at 50 mph it takes 2 hours--we divide the distance by the speed. In symbols, if `ds = vAve * `dt then `dt = `ds/vAve. Also note that (cm/s ) / s = cm/s^2, not sec, whereas cm / (cm/s) = cm * s / cm = s, as appropriate in a calculation of `dt. **
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21:48:07 Given time interval and distance moved how do you get average speed?
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RESPONSE --> Average speed is calculated by dividing distance moved by time interval.
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21:48:11 ** Average speed = distance / change in clock time. This is the definition of average speed. For example if we travel 300 miles in 5 hours we have been traveling at an average speed of 300 miles / 5 hours = 60 miles / hour. **
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???l?O?P????T?`???assignment # ???F?X???}??_??Physics I 06-09-2006
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21:50:42 036. `query 36
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