# A balloon of volume 120 m3 is filled with hot air, of density 38 kg-3. If the fabric of balloon weighs 12 kg, - Physics

Sum

A balloon of volume 120 m3 is filled with hot air, of density 38 kg-3. If the fabric of balloon weighs 12 kg, such that additional equipment of wt. x is attached to it, calculate the magnitude of Density of cold air is 1.30 kgm-3.

#### Solution

Volume of balloon = V = 120 m3

Density of hot air = ρ_"hot air" = 0.38 kgm-3

Mass of empty balloon = 12 kg

Weight of the empty balloon = 12 kgf

Weight of the additional equipment attached with the balloon

=x kgf

Density of cold air = ρ_"cold air" = 1.30 Kgm3

Volume of balloon=Volume of hot air inside the balloon=Volume of cold air displaced by balloon

= V = 120 mWeight of hot air = "V""p"_"hot air" g

= 120 x 0.38 x g = 45.6kgf

Weight of empty balloon + Weight of hot air inside the balloon + Weight of equipment = Downthrust

12 + 45.6 + x = Downthrust

Downthrust = 57.6 + x

Upthrust = Weight of cold air diplaced by balloon

= "V""ρ""cold air" g

= 120 x 1.30 xg= 156kgf

By law of floatation:

Downthrust = Upthrust

57.6 + x = 156

x = 156-57.6

x = 98.4 kgf

Concept: Archimedes' Principle
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#### APPEARS IN

Goyal Brothers Prakashan Class 9 A New Approach to ICSE Physics Part 1
Chapter 5 Upthrust and Archimedes’ Principle
Practice Problems 5 | Q 3