# position, acceleration, velocity

• Mar 21st 2010, 11:15 AM
FinalFantasy9291
position, acceleration, velocity
can anybody help me on my calc problem? i don't quite understand it.

The position of a particle at time t sec is s=t^3-6t^2+9t. find the particles acceleration each time the velocity is zero.

thank you.
• Mar 21st 2010, 11:52 AM
skeeter
Quote:

Originally Posted by FinalFantasy9291
can anybody help me on my calc problem? i don't quite understand it.

The position of a particle at time t sec is s=t^3-6t^2+9t. find the particles acceleration each time the velocity is zero.

thank you.

you are given s(t).

find v(t) = s'(t)

also find a(t) = v'(t) = s''(t)

set v(t) = 0, solve for t, then determine a(t) for those time(s)
• Mar 21st 2010, 01:24 PM
FinalFantasy9291
could you start the problem out for me? i still don't really know how to start.
• Mar 21st 2010, 01:29 PM
skeeter
Quote:

Originally Posted by FinalFantasy9291
could you start the problem out for me? i still don't really know how to start.

are you saying that you do not know how to find the derivative of a polynomial function?
• Mar 21st 2010, 01:45 PM
FinalFantasy9291
ooh! okay. well i took the derivative of s(t) and then i took the double derivative.

the double is 6t-12 right?

and then i set s'(t) to 0 so i got t=3 and t=1

then i pluged them both into a(t) and got 6 and -6.

did i do it right? :D
• Mar 21st 2010, 01:57 PM
skeeter
Quote:

Originally Posted by FinalFantasy9291
ooh! okay. well i took the derivative of s(t) and then i took the double derivative.

the double is 6t-12 right?

and then i set s'(t) to 0 so i got t=3 and t=1

then i pluged them both into a(t) and got 6 and -6.

did i do it right? :D

yes