Uniform Motion - Average Speed

Define the relationship between speed, distance, and time.

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Answer explanation

Speed is the rate at which an object covers distance over time. The relationship is defined by the formula: Speed = Distance / Time. Thus, to find distance, multiply speed by time, and to find time, divide distance by speed.

Tags

NGSS.MS-PS3-1

What is the formula used to calculate speed?

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Answer explanation

The formula to calculate speed is speed = distance / time. This means that speed is determined by dividing the total distance traveled by the time taken to travel that distance.

A cyclist rides 90 kilometers in 3 hours. The cyclist’s average speed is (a)  

• 10 km/h
• 15 km/h
• 30 km/h
• 45 km/h

Answer explanation

To find the average speed, divide the total distance by the total time. Here, 90 km ÷ 3 hours = 30 km/h. Thus, the cyclist’s average speed is 30 km/h.

A car is traveling at a constant speed of 72 km/h. How far can it travel in 5 hours?

• 360 km
• 300 km
• 420 km
• 540 km

Answer explanation

To find the distance traveled, use the formula: distance = speed × time. Here, speed = 72 km/h and time = 5 hours. Thus, distance = 72 km/h × 5 h = 360 km. The car can travel 360 km in 5 hours.

Calculate how long it will take for a boat to travel a distance of 250,000 meters at a speed of 50 m/s.

• 1000 s

• 1250 s

• 5000 s

• 10,000 s

Answer explanation

To find the time, use the formula: time = distance / speed. Here, time = 250,000 m / 50 m/s = 5,000 s. However, the correct answer is 1,250 s, indicating a possible error in the question or options.

A train travels 450 meters in 90 seconds. What is the train’s average speed?

• 2.5 m/s

• 5 m/s

• 10 m/s

• 20 m/s

Answer explanation

To find the average speed, divide the distance by the time. Here, 450 meters ÷ 90 seconds = 5 m/s. Therefore, the train’s average speed is 5 m/s.

Tags

NGSS.MS-PS3-1

An airplane flies at a speed of 700 m/s. If the distance around the Earth is approximately 40,000,000 meters, how long will it take the airplane to fly around the Earth?

• 50,000 seconds
• 57,142.857 seconds
• 60,000 seconds
• 70,000 seconds

Answer explanation

To find the time, divide the distance by speed: 40,000,000 m ÷ 700 m/s = 57,142.86 seconds. Thus, it will take approximately 57,143 seconds for the airplane to fly around the Earth.

A tsunami travels at an average speed of 120 m/s. How far will it travel in 10,000 seconds?

• 1,000,000 meters
• 800,000 meters
• 1,500,000 meters
• 1,200,000 meters

Answer explanation

To find the distance a tsunami travels, use the formula: distance = speed × time. Here, speed = 120 m/s and time = 10,000 s. Thus, distance = 120 m/s × 10,000 s = 1,200,000 meters.

A car travels at an average speed of 80 km/h for 2.5 hours. Calculate the distance it covers.

• 150 km
• 250 km
• 300 km
• 200 km

Answer explanation

To find the distance, use the formula: Distance = Speed × Time. Here, Speed = 80 km/h and Time = 2.5 hours. Thus, Distance = 80 × 2.5 = 200 km. The car covers 200 km.

True or False: It is possible for an object to travel at a perfectly constant speed in real life.

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Answer explanation

False: In real life, factors like friction, air resistance, and other forces make it impossible for an object to maintain a perfectly constant speed. Speed can only be constant in idealized conditions.