Answer
b) Equilibrium Length = 8
c) Shortest length = 6
d) Longest Length = 10
Work Step by Step
Length of spring at any time is given by
$L = 8 - 2 \cos (4\pi t)$
b) Equilibrium Length
It is the original length of the spring = 8, when $\cos (4\pi t) = 0$
$- 2 \cos (4\pi t)$ is the oscillation part
c) Shortest length
L_shortest = 8 - 2= 6, when $\cos (4\pi t) = 1$
d) Longest Length
L_longest = 8 + 2 = 10 when $\cos (4\pi t) = -1$
