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Acceleration in Drag Racing

Date: 06/06/2002 at 02:21:18
From: Tim Fraser
Subject: drag racing

A drag race car starts from a dead stop. It travels 1/4 mile in 11.0 
seconds. What is the MPH formula? 

Every time I try to figure out the answer I come up with an average 
speed. As if the speed were the same at finish as it was at start!

I realize it must be some type of curve, but I never took trig or calc.
Any help would be greatly appreciated.

Date: 06/06/2002 at 14:31:48
From: Doctor Ian
Subject: Re: drag racing

Hi Tim,

Assuming that the acceleration is constant (which it probably 
isn't!), the equation would be 

  distance = (1/2) * acceleration * time^2

For your example, that's 

  5280/4 feet = (1/2) * a * (11 sec)^2

                5280/4 feet
            a = ---------------
                (1/2) 121 sec^2

              = 21.8 feet/sec^2

So after 1 second, it's going about 22 feet per second.  After 2 
seconds, about 44 feet per second.  After 11 seconds, it would be 
going 242 feet per second... which is about

                    60 miles/hour
  242 feet/second * -------------- = 165 miles/hour
                    88 feet/second

Does this help? 

- Doctor Ian, The Math Forum 
Associated Topics:
High School Physics/Chemistry

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