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# Physics buoyant force questions.?

How do you find the buoyant force at sea level? What is the formula I'd use?

...Larry Walters ascended from his home in long beach to an altitude of 4900m (16000 ft) after tying 42 helium filled, 1.9 m diameter weather ballons to his patio chair. show that the buoyant force on these at sea level would be 1800 N

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- billrussell42Lv 79 years agoFavorite Answer
Buoyancy of helium is the difference between the density of He and of air.

Density of Helium gas 0.18 kg/m³

Density of Air 1.204 kg/m³

subtract the two to get about 1.02 kg/m³

but this depends on temperature.

each balloon has a volume of

V = ⁴/₃πr³ = ⁴/₃π(0.95)³ = 3.6 m³

x42 that is 151 m³

1.02 kg/m³ x 151 m³ = 154 kg

converting to N, that is 1500 newtons

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