What equation to use?

Question

The earth has a 4000-mile radius and rotates one revolution every 24 hours. What is the linear speed of a point on the equator, in mph?

answer: 1047 mph

Answer 1

Circumference

C = 2 π r

c = 2(3.141592654)(4000)

c = 6.283185307(4000)

c = 25132.74123

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There is 24 hours in a day
d = rt

d / t = r . . . use this formula

25132.74123 / 24 = 1074.197551 mph

The answer is 1074.3 mph rounded to one decimal place.

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Answer 2

Speed is the amount of distance you travel in a certain amount of time.

What's the distance you're traveling here? Well, you're going once around the equator. The equator is a circle of radius 4000 miles, so the distance around the circle is 2*pi*(4000 miles).

What's the time it takes to travel that distance? 24 hours, obviously.

Take 2*pi*(4000 miles) and divide it by 24 hours, and you'll have your answer.