Traveling speed

Question

A car is traveling at a speed of 90 miles per hour. What is the car's speed in feet per second? How many feet will the car travel in 15 seconds? In your computations, use the fact that 1 mile is equal to 5280 feet. Do not round your answers.

Answer 1

Start with (90 miles / hour) and multiply it by things that are equal to 1 until you get it in the units that you want (feet / second)  

 

Note that 1 mile = 5280 feet  and  1 hour = 60 minutes = 60*60 seconds = 3600 seconds 

 

(90 miles / hour) * (5280 feet / 1 mile) * (1 hour / 3600 seconds)  =  

 

(90*5280)/3600 in units of feet / second  =  

 

132 feet per second  

 

Note how the units of miles cancel because there is 1 in the numerator and 1 in the denominator.  The same is true for the units of hours.