Uniform Motion - Average Speed

Define the relationship between speed, distance, and time.

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?

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.

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.