Question

use the graph below to answer questions 6 - 7 about the cyclist.

1. during what time interval was the cyclist not moving forward?

a. 10 - 15 minutes
b. 15 - 30 minutes
c. 0 - 5 minutes
d. 5 - 10 minutes

1. compare the slope of the graph from 5 - 10 minutes to 20 - 25 minutes. what can you do with the slopes?

a. the cyclist is moving at the same speed during both times.
b. you cannot use slope to compare speed.
c. the cyclist is moving faster at 5 - 10 minutes.
d. the cyclist is moving slower from 5 - 10 minutes.

1. the length of a path between two points is called

a. velocity.
b. distance.
c. speed.
d. relative motion.

1. it can be important to know the velocity of an object, not just its speed, because

a. speed is always an average.
b. velocity also tells direction.
c. speed is useful only for fast - moving objects.
d. velocity also tells acceleration.

Explanation:

Step1: Analyze when distance doesn't change

On a distance - time graph, when an object is not moving forward, the distance remains constant over time. Looking at the graph, from 10 - 15 minutes, the distance is 3 km and does not increase.

Step2: Analyze slopes for speed comparison

The slope of a distance - time graph represents speed. For 5 - 10 minutes: The distance changes from 1 km to 3 km in 5 minutes. The slope $m_1=\frac{3 - 1}{10 - 5}=\frac{2}{5}$ km/min. For 20 - 25 minutes: The distance changes from 3 km to 4 km in 5 minutes. The slope $m_2=\frac{4 - 3}{25 - 20}=\frac{1}{5}$ km/min. Since $m_1>m_2$, the cyclist moves faster from 5 - 10 minutes.

Step3: Recall definitions

The length of a path between two points is called distance. Velocity is speed with direction, speed is distance per time, and relative motion is the motion of an object with respect to another object.

Step4: Recall velocity concept

Velocity is important because it tells both speed and direction. Speed only gives the magnitude of how fast an object is moving.

Answer:

1. A. 10 - 15 minutes
2. C. The cyclist is moving faster at 5 - 10 minutes.
3. B. distance
4. A. velocity also tells direction