Answer:
period = 0.65 sec
Explanation:
from the question we are given the following
extension (x) = 2.6 cm = 0.026 m
mass of object (Mo) = 7 g = 0.007 kg
mass of block (Mb) = 28 g = 0.028 g
acceleration due to gravity (g) = 9.8 m/s^{2}
period = 2π x
where k is the spring constant of the spring
and k = \frac{Mo x g}{x}
k = \frac{0.007 x 9.8}{0.026}
k = 2.64 N/m
now period = 2π x
period = 0.65 sec