Test 1 Fall 2008

# Test 1 Fall 2008 - PHYS 2211, Test 1, September 18, 2008...

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PHYS 2211, Test 1, September 18, 2008 Name (print)Key-EFG Instructions Read all problems carefully before attempting to solve them. Your work must be legible, and the organization must be clear. You must show all work, including correct vector notation. Correct answers without adequate explanation will be counted wrong. Incorrect work or explanations mixed in with correct work will be counted wrong. Cross out anything you don’t want us to read! Make explanations correct but brief. Don’t write a lot of prose. Include diagrams! Show what goes into a calculation, not just the Fnal number, e.g.: a · b c · d = (8 × 10 - 3 )(5 × 10 6 ) (2 × 10 - 5 )(4 × 10 4 ) =5 × 10 4 Give standard SI units with your results. Unless specifcally asked to derive a result, you may start ±rom the ±ormulas given on the ±ormula sheet, including equations corresponding to the ±undamental concepts. I± a ±ormula you need is not given, you must derive it. I± you cannot do some portion o± a problem, invent a symbol ±or the quantity you can’t calculate (explain that you are doing this), and use it to do the rest o± the problem. Honor Pledge “In accordance with the Georgia Tech Honor Code, I have neither given nor received unauthorized aid on this test.” Sign your name on the line above

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Problem 1 (25 Points) 0 2 4 6 8 10 100 80 60 40 20 0 20 40 60 80 100 t p y (t) (a, 6 pts) Consider the parabolic motion (in the x-y coordinate system) of a cannonball in the presence of the Earth’s gravitational Feld. If the Y-component of the momentum, p y , changes with time, t , (as shown in the graph above) why is p y changing sign? Defne our system to be the cannonball and the surroundings to be the earth. -→ F net = ± 0 , - mg, 0 ² and by the momentum principle, Δ p y = - mg Δ t , we see that p y is changing with time. From the graph we see that the initial momentum o± the cannonball, p y, 0 , is positive. The momentum o± the cannonball will remain positive until the ball reaches the top o± its trajectory because it is raising along the positive Y-direction. The change in sign occurs when the ball travels along the direction o± the net ±orce, which is the negative Y-direction. (b, 6 pts) Why does p y depend linearly on time and why is the slope negative? p y will depend linearly on time because gravity and the mass o± the cannonball are constant. This implies that the solution to the momentum equation given in (a) is p y ( t )= - mgt + p 0 .
(c, 6 pts) On the graph below, draw the time evolution of the Y-component of the cannonball’s position.

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## This note was uploaded on 09/12/2011 for the course PHYS 2211 taught by Professor Prog during the Spring '09 term at Georgia Institute of Technology.

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Test 1 Fall 2008 - PHYS 2211, Test 1, September 18, 2008...

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