PHYS-1100 Fall 2009 Exam 3 answer key

# PHYS-1100 Fall 2009 Exam 3 answer key - 1 In the Olympic...

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1. In the Olympic 100 m sprint events, an athlete reaches nearly his or her maximum speed within the first few strides. Suppose an 80 kg sprinter achieves a speed of 9.0 m/s within the first half dozen strides of the race, requiring about 2.0 seconds out of the entire race, which will last no more than perhaps 10 or 11 seconds. What average force is required to accelerate the sprinter during those first two seconds? a) 780 N (6) b) 360 N c) 210 N d) 80 N e) none of the above are even approximately correct 2. Only three forces act upon a 10 kg object, which is moving in a straight line with a steady speed. One force has magnitude 200 N and points in the positive x -axis direction, a second force has magnitude 300 N and points in the negative y -axis direction. What is the approximate magnitude of the third force? a) 500 N b) 100 N c) 980 N (6) d) 360 N e) none of the above are even approximately correct 3. What is the direction of the third force on the object in problem 2, expressed as an angle measured counterclockwise from the positive x -axis? (6) a) 124º b) 56 º (2) c) 304 º d) 135 º e) none of the above are even approximately correct

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4. Two 1.7 kg pythons remain at rest on a ramp that is inclined 22º above the horizontal ( i.e ., snakes , on an inclined plane ). Is the magnitude of the normal component of the force that each snake exerts on the ramp greater than, less than, or equal to the weight of that snake? a) greater than (6) b) less than c) equal to d) yes 5. Released from rest, a 1.7 kg python, on a different ramp that is also inclined 22º above the horizontal, slides down the ramp with increasing speed. From this observation you can properly infer that a) the coefficient of kinetic friction is about 0.40
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PHYS-1100 Fall 2009 Exam 3 answer key - 1 In the Olympic...

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