Question

A rubber balloon of negligible mass is filled with \[500g\] of water. Its weight in water will be:
A. 250g
B. 500g
C. Zero
D. 100g

Answer 1

Hint: To find the weight of the balloon in the water we will find whether the force applied on the balloon from the balloon to the water surface and from the water surface to the balloon is equal or not. The condition for the balloon to float in a particular liquid is when the density of both the balloon and liquid are the same or the balloon's density is lower than that of the balloon.

Complete step by step answer:
A balloon of negligible mass and is filled with water, now the balloon whose weight is \[500g\] and is filled with water is weighed at \[500g\]. The density of the water in the balloon is the same as that of the density of the water the balloon is kept in.
Now as the balloon floats on the water surface and when the force in terms of the weight of the balloon is resisted by the upward force or buoyant force of the water exerted on the balloon. The buoyant force of the water is inversely proportional to the force or weight exerted by the balloon on the water surface and for the balloon to float both the densities of the balloon and balloon should be same thereby for the balloon to float as we can see that the balloon has no weight of its own thereby no greater density the density of both the water in the balloon and water surface are same making the balloon float in the water. Hence, the weight of the balloon in the water will be zero.


Note:
A body will only float when the density of the object is either lower or same as that of the density of the liquid the object floated into.