Posted by **rudy** on Sunday, April 27, 2008 at 11:35pm.

im trying to take the derivative of this problem and plug in seven but im not getting the answer.

s=t3–2t2–6t t> or equal to 0

where s is measured in meters and t in seconds. When does the particle reach a velocity of 7 m/s?

- math -
**Reiny**, Monday, April 28, 2008 at 12:09am
ds/dt = 3t^2 - 4t - 6

so when ds/dt = 7

3t^2 - 4t - 6 = 7

3t^2 - 4t - 13 = 0

Solve using the quadratic equation, and use the positive answer.

(I got 2.85 sec)

- math -
**stephen**, Thursday, November 22, 2012 at 10:18pm
if I am driving a car at 100km / hr and my reaction time is 0.382 seconds.

with many thanks Stephen

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