Unit 3 Review #2 (7.7 ABC)

What is the formula to calculate average speed?

Answer explanation

The correct formula for average speed is \( \text{Average Speed} = \frac{\text{Total Distance}}{\text{Total Time}} \). This means average speed is calculated by dividing the total distance traveled by the total time taken.

Which of the following best describes the difference between distance and displacement?

• Distance is a vector quantity, while displacement is a scalar quantity.

• Distance is the total path traveled, while displacement is the shortest path between two points.

• Distance includes direction, while displacement does not.

• Distance is always equal to displacement.

Answer explanation

The correct choice states that distance is the total path traveled, while displacement is the shortest path between two points. This highlights that distance is a scalar quantity, whereas displacement is a vector quantity.

A car travels 150 km in 3 hours. What is its average speed?

• 45 km/h

• 50 km/h

• 55 km/h

• 60 km/h

Answer explanation

To find the average speed, divide the total distance by the total time. Here, 150 km ÷ 3 hours = 50 km/h. Thus, the average speed of the car is 50 km/h.

How can you differentiate between speed and velocity?

• Speed is a vector quantity, while velocity is a scalar quantity.

• Speed includes direction, while velocity does not.

• Speed is the rate of change of distance, while velocity is the rate of change of displacement.

• Speed is always greater than velocity.

Answer explanation

Speed measures how fast an object moves regardless of direction (rate of change of distance), while velocity includes direction (rate of change of displacement). Thus, the correct choice highlights this distinction.

In a distance-time graph, what does a horizontal line represent?

• Constant speed

• Increasing speed

• Decreasing speed

• No motion

Answer explanation

A horizontal line on a distance-time graph indicates that the distance does not change over time, meaning there is no motion. Therefore, the correct answer is 'No motion'.

A runner completes a 400 m lap in 50 seconds. What is the runner's average speed?

• 6 m/s

• 7 m/s

• 8 m/s

• 9 m/s

Answer explanation

To find the average speed, divide the distance by the time. The runner covers 400 m in 50 seconds. Average speed = 400 m / 50 s = 8 m/s. Thus, the correct answer is 8 m/s.

Tags

NGSS.MS-PS3-1

Which scenario best illustrates the concept of displacement?

• A car travels 10 km north, then 10 km south.

• A person walks 5 km around a circular track.

• A bird flies 3 km east and then 4 km north.

• A train moves 20 km in a straight line.

Answer explanation

Displacement measures the shortest distance from the starting point to the ending point. The bird's path creates a right triangle, resulting in a net displacement of 5 km, while the other options either return to the start or move in a loop.

If a cyclist travels 30 km in 2 hours and then 20 km in 1 hour, what is the cyclist's average speed for the entire trip?

• 15 km/h

• 16.67 km/h

• 20 km/h

• 25 km/h

Answer explanation

The total distance is 30 km + 20 km = 50 km. The total time is 2 hours + 1 hour = 3 hours. Average speed = total distance / total time = 50 km / 3 hours = 16.67 km/h, which is the correct answer.

How does a distance-time graph with constant speed differ from one with changing speed?

• Constant speed is shown by a curved line, while changing speed is shown by a straight line.

• Constant speed is shown by a straight line, while changing speed is shown by a curved line.

• Both are shown by straight lines but with different slopes.

• Both are shown by curved lines but with different curvatures.

Answer explanation

A distance-time graph with constant speed is represented by a straight line, indicating uniform motion. In contrast, a graph with changing speed is shown as a curved line, reflecting variations in speed over time.

Tags

NGSS.MS-PS3-1

A car travels 60 km east and then 80 km west. What is the car's displacement?

• 20 km east

• 20 km west

• 140 km

• 0 km

Answer explanation

The car travels 60 km east and then 80 km west. The net movement is 80 km west - 60 km east = 20 km west. Thus, the displacement is 20 km west.