Question

A balloon filled with hydrogen rises upwards.

• A. hydrogen is an element
• B. the pressure inside the balloon is greater than the atmospheric pressure
• C. hydrogen is a colourless gas
• D. the weight of the balloon is less than the weight of the air displaced by it

Answer 1

The correct option is D

the weight of the balloon is less than the weight of the air displaced by it

Explanation for correct option(s):

Option (D) :

1. A balloon filled with hydrogen or hot air weighs less than the weight of the air it displaces.
2. The upthrust is, therefore, greater than its weight and the resultant upward force on the balloon causes it to rise.
3. The balloon does not rise indefinitely, because as it goes up, it encounters air with low density.
4. As a result, the weight of the displaced air becomes less. When the weight of the air displaced becomes equal to the weight of the balloon it does not experience any upthrust, thus it becomes stationary at that height.

Hence, Option(D) is correct.