Need some help regarding a density question

1. Mar 23, 2005

forcedphysics

a helium balloon, with a combined mass of the balloon and helium of 20kg, is used to lift a payload of 70kg. At an altitude of 30 km the balloon stops and remains stationary.

a. Explain
b. at 30km, the density of air os 0.035kg/m^3. What is the volume of the balloon assuming that the volume of the payload is 0.010m^3

can someone plz help, i need to kinda have a idea for my quiz tomorrow

for the vlume i came up with v=m/density

v = 90/.035

v = 2571???

Last edited: Mar 23, 2005
2. Mar 23, 2005

tigger

I think you should use the concept of Buoyancy Force to solve it..
Balance the buoyancy force and the total weight to get the volume of the balloon and payload, then substract the volume of payload..

3. Mar 23, 2005

HallsofIvy

Staff Emeritus
At 30 km, the total force, weight and bouyancy, is 0. You know the weight so you can calculate the bouyancy force- you also know, or should know, that that is equal to the weight of air displaced by the baloon. You are given the volume of the baloon- what would be the weight of that volume of air?