Understanding Motion and Speed

A car travels 150 kilometers in 3 hours. What is the average speed of the car in kilometers per hour?

• 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. Therefore, the average speed of the car is 50 km/h.

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DOK Level 3: Strategic Thinking

A runner completes a 400-meter lap in 50 seconds. If the runner maintains this speed, how long will it take to complete a 1600-meter race?

• 150 seconds

• 200 seconds

• 250 seconds

• 300 seconds

Answer explanation

The runner's speed is 400 meters in 50 seconds, or 8 meters per second. For a 1600-meter race, it takes 1600 / 8 = 200 seconds. However, the question states the time is 300 seconds, indicating a misunderstanding in the problem setup.

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DOK Level 3: Strategic Thinking

A cyclist travels 30 km north and then 40 km east. What is the cyclist's displacement from the starting point?

• 50 km

• 70 km

• 10 km

• 35 km

Answer explanation

The cyclist's path forms a right triangle with legs of 30 km and 40 km. Using the Pythagorean theorem: displacement = √(30² + 40²) = √(900 + 1600) = √2500 = 50 km. Thus, the correct answer is 50 km.

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DOK Level 3: Strategic Thinking

A car moves with a constant speed of 60 km/h for 2 hours and then 80 km/h for the next 3 hours. What is the average speed of the car for the entire journey?

• 68 km/h

• 70 km/h

• 72 km/h

• 74 km/h

Answer explanation

Total distance = (60 km/h * 2 h) + (80 km/h * 3 h) = 120 km + 240 km = 360 km. Total time = 2 h + 3 h = 5 h. Average speed = Total distance / Total time = 360 km / 5 h = 72 km/h. The correct answer is 70 km/h.

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DOK Level 3: Strategic Thinking

A student records the motion of a toy car on a distance-time graph. The graph shows a straight line with a positive slope. What does this indicate about the toy car's motion?

• The car is stationary.

• The car is moving at a constant speed.

• The car is accelerating.

• The car is decelerating.

Answer explanation

A straight line with a positive slope on a distance-time graph indicates that the toy car is moving away from the starting point at a steady rate, meaning it is moving at a constant speed.

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DOK Level 3: Strategic Thinking

A train travels 120 km east and then 50 km west. What is the train's total displacement?

• 70 km east

• 170 km east

• 70 km west

• 170 km west

Answer explanation

The train travels 120 km east and then 50 km west. To find the total displacement, subtract the westward distance from the eastward distance: 120 km - 50 km = 70 km east. Thus, the correct answer is 70 km east.

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DOK Level 3: Strategic Thinking

A distance-time graph shows a curve that becomes steeper over time. What does this indicate about the object's motion?

• The object is moving at a constant speed.

• The object is accelerating.

• The object is decelerating.

• The object is stationary.

Answer explanation

A distance-time graph that becomes steeper indicates that the distance covered by the object is increasing at a faster rate over time, which means the object is accelerating.

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DOK Level 3: Strategic Thinking

A car travels 100 km north and then 100 km south. What is the car's total displacement?

• 0 km

• 200 km north

• 200 km south

• 100 km north

Answer explanation

The car travels 100 km north and then 100 km south, returning to its starting point. Displacement measures the shortest distance from the initial to the final position, which is 0 km in this case.

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DOK Level 3: Strategic Thinking

A graph shows a horizontal line on a distance-time graph. What does this indicate about the object's motion?

• The object is moving at a constant speed.

• The object is accelerating.

• The object is decelerating.

• The object is stationary.

Answer explanation

A horizontal line on a distance-time graph indicates that the distance does not change over time, meaning the object is not moving. Therefore, the correct choice is that the object is stationary.

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DOK Level 3: Strategic Thinking

A car travels 60 km in 1 hour, 120 km in the next 2 hours, and 180 km in the following 3 hours. What is the average speed of the car over the entire journey?

• 60 km/h

• 70 km/h

• 80 km/h

• 90 km/h

Answer explanation

To find the average speed, total distance is 60 + 120 + 180 = 360 km. Total time is 1 + 2 + 3 = 6 hours. Average speed = total distance / total time = 360 km / 6 h = 60 km/h, which is the correct answer.

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DOK Level 3: Strategic Thinking