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Unformatted text preview: ED –2– PHYS 2210 4. Find the regulation size (and mass, while you’re at it) for a golfball.
(a) The drag coeﬃcient cD for a golfball is (very roughly) 0.3. (Note: the c in cv 2 is given by 1 cD ρD2 )
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Calculate the numerical value of the quadratic drag constant “c” for a golf ball traveling in air, and
write down the equations of motion required to solve for x(t) and y(t) of a golfball with (just) quadratic
drag.
(b) In class we did a MMA Tutorial using NDSolve. (The code/worksheet is still available on our course
calendar for Tues Jan 25) Modify your code so that you have quadratic drag. For simplicity and
concreteness, set the angle to 45 degrees, and pick an initial speed of 80 mi/hr (converted to SI metric,
of course) Plot the trajectory for us. What is the ideal (dragfree) range in this case, and what does
your code tell you the range is including quadratic drag? (Don’t hunt for the optimum range like we
did last week, just stick with a 45 degree angle) Also, calculate what fraction of the initial speed is lost
from when you ﬁrst hit the ball (at 45 degrees) to when it lands. (Where does the lost energy go?)
(c) When I ﬁrst started thinking about this problem, I wondered whether the fractional reduction in speed
was a constant, or whether it depended on the initial velocity. What do you think? (No formal
calculation required, just make a qualitative physics argument.) Check yourself with your code, and
comment.
(d) Astronaut Alan Shepard on Apollo 14 brought a golf club with him (!) Assuming he hit it at 45 degrees
(and assuming he hit it at that same 80 mi/hr, a modest swing on earth, maybe optimistic on the
moon, given...
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This document was uploaded on 03/09/2014 for the course PHYSICS 2210 at Colorado.
 Spring '11
 STEVEPOLLOCK
 mechanics, Work, The Land

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