The average distance between earth and the sun is 1.5 ã 1011 m. (a) calculate the average speed of earth in its orbit (assumed to be circular) in meters per second. (b) what is this speed in miles per hour?

We can determine the speed of the Earth on its orbit by dividing the circumference to the period of time the Earth can complete one revolution around the Sun. First, convert years to seconds. The solutions is as follows:

V = (2πr/1 year) = (2π(1.5×10¹¹ m))÷(31536000 seconds)
V = 29,885.77 m/s

Then, 1 mile = 1609 m:

V =  (29,885.77 m/s)(1 mile/1609 m)(3600 s/1 hr)
V = 66,866.87 miles/h