I know how to begin, take the derivative.
okay that comes out to be around
So I factor out a "t"
then I set equal to "0"
and the answer should be "24/5" but it's wrong. What have I done wrong.
you made no errors in your work. the only problem is that acceleration is the 2nd derivative of position,not the first. you found the velocity equation. so just take the derivative of what you just got and solve
you have to take the second derivative and equal that to 0
Originally Posted by Zanderist
The second der. is
f ''(x)= "20t^3-72t^2"
factor out a "t"
f ''(x)= "t^2(20t-72)"
The answer is "t = 72/20"