Question

A bird on the floor of an air tight box which is being carried by a boy starts flying. The boy feels that the box is now:

• A. lighter
• B. heaver
• C. shows no change in weight
• D. lighter in the beginning and then heavier

Answer 1

The correct option is C shows no change in weight

1. Since the box is air tight no air can pass through it. So if a bird is sitting then the total weight is equal to the sum of the weight of the box and bird.
2. If the bird is flying, the reaction force applied on the floor of the box will be equal to its weight. So there will be no change in the total weight of the box. The reaction of the bird does not change as the box is air-tight.
3. Since the box is airtight its weight will not change even when birds fly inside the box. Hence, the boy feels that the box shows no change in weight.
4. The bird is placed in an airtight box. So when a force is applied by it to fly an equal force is given by the floor of the box. Due to this, the total weight of the box does not change.