if a particle moves along a line so that at time t where t [0,pi] its position is given by s(t)=-4cost-t^2/2+10 what is the velocity of the particle when its acceleration is zero?

Question

so i found
v(t) = 4sint-t
a(t)=4cost-1 = 0 solved for t plugged it into v(t) and i got the wrong answer i got 3.2 something but the choices are

-5.19
.74
1.32
2.55
8.13

please help thank you

Answer 1

Did you have your calculator set to radians ?

I get
t = arcsin(1/4)
= 1.318116

then
v(1.318116) = 4sin(1.318116) - 1.318116
= 2.55486

close to one of the choices,
(they should have rounded to 2.56)

Answer 2

3.969