Lesson 8 - Answers to Suggested Problems
After you have had a chance to try the suggested
end-of-chapter conceptual questions, problems and exercises,
you can check your answers against mine below. (Please alert
Jason Harlow jharlow@physics.utoronto.ca if you notice any
errors in the answers.)
Conceptual
Questions
13. (a) no (b) speed is minimum at the top
of the trajectory, maximum at the beginning and end of the
motion, when it returns to the same height (c) no (d) yes,
at the moment it returns to the same height
15. If wind is a factor, you want the projectile to spend
the least amount of time in the air, so the smaller angle is
preferable. If you want to increase the amount of time
the projectile is in the air, use the larger angle.
This is the case in football, when you want your defensive
players to have the maximum amount of time to run down the
field and meet the punt returners.
16. The flicked coin travels in a parabolic path and lands
some distance away from the table. The nudged coin
drops straight down. Both coins hit the floor at the
same time.
Problems and Exercises
25. x = 130 m, y = 30.9 m
27. (a) 3.50 s (b) 28.6 m/s (c) -34.3 m/s (d) 44.6 m/s, 50.2
degrees below the horizontal
30. (a) 14.2 degrees (b) 75.8 degrees, which would not be
used because the pass would take much longer as the ball
traveled way up and then down. (c) 0.60 s
34. (a) 27 m (b) 36 m (c) 20 m/s
36. 9.2 m, assuming the person is a point-particle.
50. (a) 1600 km (b) no real cannonball would go this far (c)
the range equation assumes no air resistance and flat earth,
so this equation is inapplicable (d) air resistance would be
huge for a cannonball going 4000 m/s, the maximum height
assuming no air resistance is 410 km, which is low-earth
orbit (no air), and the radius of the earth is 6400 km, so
over a distance of 1600 km you cannot ignore the curvature
of the earth.