Introduction to Physics Primer 

Lesson 8 - Answers to Suggested Problems

by Jason Harlow


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.