acceleration

Question

A car was stopped at a red light. When the light turns green, the car reaches a speed of 22 miles per hour in 3 seconds. What is the acceleration, to 1 decimal place?

Answer 1

The speed is given in miles per HOUR while the time is given in SECONDS.  You need to put them into the same units.  Lets convert 3 seconds to hours:

 

     (3 sec)*(1 hour/3600 sec) = 1/1200 hour

 

     Acceleration = (change in speed)/(change in time) = (22 - 0)/(1/1200 - 0) = 22*1200 = 26,400 mi/hour²

 

So if you continue to accelerate at that rate for one hour, rather than for 3 seconds, you will reach a speed of 26,400 mph.  For reference, the speed needed to escape Earth's gravity is about 25,000 mph.  No cars can sustain that acceleration rate for long, however.