Drag racing combines the reflexes of the driver with a powerful engine to propel

Question

Drag racing combines the reflexes of the driver with a powerful engine to propel a specially designed car across a quarter mile as quickly as possible. After a series of lights to prepare the driver, a green light signals the drivers to go. The car accelerates uniformly at 18 m/s2 for the first 5 seconds, at which point the driver injects nitrous oxide into the engine to boost the acceleration of the car to 29 m/s2.

How fast is the car going as it crosses the finish line? ______m/s

What is the time for the car to go the quarter-mile? ______s

Explanation / Answer

1/4 mile = 402.3 mts

a. distance covered in first 5 sec =

S=ut+0.5*a*t^2

S=0.5*18*25 = 225 mts

speed after 5 sec=

v=u+at

v=18*5 = 90 m/s

distance remaining to cover = 402.3-225 = 177.3 mts

v2=u2 + 2aS

v2=902+2*29*177.3

v=135.585 m/s

b. v=u+at

135.585=90+29*t

t=1.57 sec

total time = 1.57+5 = 6.57 sec

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