# Homework Help: Accerelation of balloon

1. May 9, 2015

### aopaop03

1. An empty spherical weather balloon with a mass of 5 kg has a radius of 2.879 m when fully inflated with helium. It is supposed to carry a small load of instruments having a mass of 10 kg. Taking air and helium to have densities of 1.16 kg/m^3, respectively, what will be the acceleration of the balloon and load immediately after it is released?

upward force :FB=ρairVg
downward force: Mg=(5+10+ρHeV)g
so FB-Mg=Ma
i find that a>g can balloon have accerelate more than g? or I do something wrong?

2. May 9, 2015

### SteamKing

Staff Emeritus
Why do you think having a > g would be wrong? Remember, the acceleration of the balloon and the direction of g should be opposite one another.

Also, the problem statement was to have the densities of both air and helium mentioned, but only one figure is given, and it's not clear for which gas it is.

3. May 9, 2015

### jbriggs444

A trick answer to this question s -9.8 meters/second2

The balloon is specified as being empty. It has no lift.