#1
Elastic force on the balloon
F = kx
here we know that
k = 115 N/m
x = 0.8 m
F = 115 N/m (0.8m) = 92 N
#2
Elastic potential energy


U = 36.8 J
#3
By energy conservation
initial kinetic energy = final potential energy
U = KE

#4
as we know that


by solving above equation we have
