Kinematics - Finding position and acceleration

[MozAngeles]

Homework Statement

The position of the front bumper of a test car under microprocessor control is given by x(t) = 2.17 m + 4.80 m/s²t² - 0.100 m/s⁶t⁶.
a. Find its position at the first instant when the car has zero velocity.
b. Find its acceleration at the first instant when the car has zero velocity.
c. Find its position at the second instant when the car has zero velocity.
d. Find its acceleration at the second instant when the car has zero velocity.

Homework Equations

i took the derivative and to get v(t) for parts a,b,c of this
then the second derivative to get a(t)

The Attempt at a Solution

a(t)= 9.6-3t⁴ solve for t we get 1.337 when i plug that into the v(t) equation i get ~10 but when i plugg this in it's wrong. I have to idea what is going wrong, this is how my professor set it up... i got a,b,c right though...

 

[rickz02]

Are you not suppose to solve for t at v(t) = 0?

 

[MozAngeles]

yes for part a and c