Question

An air-tight cage with a parrot sitting in it is suspended from the spring balance. The parrot starts flying. The reading of the spring balance will

• A. increase
• B. decrease
• C. not change
• D. be zero

Answer 1

The correct option is C not change

Here cage is air-tight, that means air cannot escape.

When a parrot is sitting in a cage, reading of balance will be an addition of weights of parrot and cage.

When parrot starts flying, to be in the air, it must push air in cage downwards with fore equal to it's weight.

So, base of cage now have air pushing it downwards with force equal to mass of parrot.

So, reading now is weight of cage and force of air (which is same as weight of parrot)

So, reading remains same.

Option C is correct.