Solve Buoyancy Problem: Estimate Balloon Radius for 6 Yr Old Boy

[lavster]

Homework Statement

A six year old boy weights about 25 kg. Estimate the radius of a spherical helium balloon capable of lifting the boy.Solution 2.

Homework Equations

V=(4/3)*pi*r^3.

B= density of air* volume *g if in air

The Attempt at a Solution

the buoyancy must be greater than the weight.
Density of helium is 4g/22.4l = 0.180 kg/m3.
Density of air (Nitrogen) is 28g/22.4l = 1.25 kg/m3.


not sure where to go from here...

thanks

 

[lavster]

never mind I've got it now :)