Answer:
a = 132 m/s^2
Explanation:
f(t) = t^4 − 2t^3 − 6t^2 + 9t
v = f'(t) = 4t^3 - 6t^2 - 12t + 9
a = f''(t) = 12t^2 - 12t -12
Substitute t = 4 seconds into the equation for a:
a = 12(16) -12(4) -12 = 132 m/s^2