Answer:
0.20, 0.36 seconds
Explanation:
We have already seen that the equation for y(t) can be written as ...
y(t) = √29·sin(4πt +arctan(5/2))
The sine function will have a value of -1/2 for the angles 7π/6 and 11π/6. Then the weight will be halfway from its equilibrium position to the maximum negative position when ...
4πt +arctan(5/2) = 7π/6 or 11π/6
t = (7π/6 -arctan(5/2))/(4π) ≈ 0.196946 . . . seconds
and
t = (11π/6 -arctan(5/2))/(4π) ≈ 0.363613 . . . seconds
The weight will be halfway from equilibrium to the maximum negative position at approximately 0.20 seconds and 0.36 seconds and every half-second thereafter.