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3v^2 2d d=------- and t= ------ 20 [#permalink]
09 Sep 2003, 07:09
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3v^2 2d
d=------- and t= ------
20 v
d is the distance traveled, in meters, after the brakes are applied.
v is the velocity, in meters per second, before the brakes are applied.
t is the time, in seconds, it takes to stop after the brakes are applied.
The formulas above are used to compute the distance a car travels after the brakes aree applied. If the driver of a car applied the brakes just as a traffic light turned yellow and stopped exactly 6 seconds later, what is the values of v?
a) 20
b) 80
-----
3
c) 30
d) 40
e) 60 The answer is A
Thanks!!
Mystery
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Intern
Joined: 17 Aug 2003
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The equations are not written out clearly but i assume you mean
d=(3v^2)/20 and t=2d/v
in which case from the second equation:
d=vt/2
if you substitute this into the first equation:
vt/2 = (3v^2)/20
20vt = 6v^2
v = 20t/6
we know t=6
therefore v=20
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