Here elastic balloon launcher will behave like an ideal spring
so here we have
spring constant k = 115 N/m
mass of balloon = 1.3 kg
Part a)
Stretch in the band is given as
x = 0.8 m
now the force on the balloon is given by
F = k x
now from above
so it will exert 92 N force on it
Part b)
Elastic potential energy is given as
so here we have
Part c)
Here in this case we can say that kinetic energy gained by the balloon must be same as the elastic potential energy stored in the rubber because there is no energy loss in this system
So kinetic energy = 36.8 J
Part d)
As we know by the formula of kinetic energy
so speed of the balloon will be 7.52 m/s