Question

For questions 9 through 11, refer to the graph below.
9. Draw a point on the graph that represents 200 m traveled in
4 seconds. Draw a line connecting this point with the origin (0,0).
Label this as line A.
10. Draw a point on the graph that represents 100 m traveled in
10 seconds. Draw a line connecting this point with the origin (0,0).
Label this as line B.
11. Calculate the average speed (slope) of lines A and B. Be sure to
include units.
Velocity (page 336)
12. How do speed and velocity differ?
13. Circle the letter of each sentence that describes a change
in velocity.
a. A moving object gains speed.
b. A moving object changes direction.
c. A moving object moves in a straight line at a constant speed.
d. A moving object slows down.
14. Is the following sentence true or false? If a car travels around a
gentle curve on a highway at 60 km/h, the velocity does not
change.
Combining Velocities (page 337)
15. How do velocities combine?
16. A river flows at a velocity of 3 km/h relative to the riverbank. A
boat moves upstream at a velocity of 15 km/h relative to the river.
What is the velocity of the boat relative to the riverbank?
a. 18 km/h downstream
b. 15 km/h upstream
c. 12 km/h upstream
d. 12 km/h downstream

Answer 1

9. Point at (4 s, 200 m). Draw line from (0,0) to (4,200). Label it A.

10. Point at (10 s, 100 m). Draw line from (0,0) to (10,100). Label it B.

11. Average speed = slope = change in distance / change in time.
- Line A: slope = 200 m / 4 s = 50 m/s.
- Line B: slope = 100 m / 10 s = 10 m/s.

12. Speed is a scalar (magnitude only). Velocity is a vector: it includes both speed and direction.

13. Sentences that describe a change in velocity: a, b, d (gain speed; change direction; slow down). c does not (constant speed in straight line).

14. False. Even at constant speed the direction changes on a curve, so velocity changes.

15. Velocities combine by vector addition (add their components or use head-to-tail vector sum).

16. Relative to the bank: v_boat/bank = v_boat/river + v_river/bank. Upstream 15 km/h plus river 3 km/h downstream gives 15 − 3 = 12 km/h upstream. Answer: c.