Considering that no initial velocity was imparted to the hamburger, then we can use the distance covered formula for motion under constant acceleration (that of gravity) and solve for the time it took to reach the ground.
D = vi * t + (1/2) a * t^2
in our case
19 = 0 + 4.9 t^2
t^2 = 19/4.9
then t is approximately 1.97 seconds
We now use this time information in the equation for velocity under accelerated motion (due to gravity)
carbon dioxide (what you are blowing up the balloon with) is a heavy gas. so when you fill the Balloon with it, the balloon will not float. helium is a light gas and floats. gravity takes another. part in this
