How do you convert 90 miles per hour into feet per second?

Answer 1

You need to know the conversion rates for both miles to feet AND hours to seconds. There are 5280 feet in a mile and 3600 seconds in an hour.

90mi/1hr (5280 ft/mi)(hr/3600 s)

You want the units to cancel out, so that's how you decide to put mi and hr in the numerator or the denominator. For miles to cancel out, it has to be in the denominator of the conversion factor and vice versa for hours. After the units cancel out, you're left with:

(90)(5280 ft)/(3600 s) = 475200 ft/3600 s = 132 ft/s