Calculus. please show work

Question

A particle moves along a line so that at time 𝑡, where 0 ≤ 𝑡 ≤ 𝜋, its position is given by

𝑠(𝑡) = −4 cos 𝑡 − 𝑡²/2 + 10. What is the velocity of the particle when its acceleration is zero

Answer 1