Question

If a parrot starts flying upwards with an acceleration in an airtight cage, then the boy will feel the weight of the cage:
A. Unchanged
B. Reduced
C. Increased
D. Nothing can be said

Answer 1

Hint: While we travel in a lift that goes down we feel that we have lost some weight and when lift goes up we feel weight gain. But the actual mass of us is the same in both cases. It's all due to the variation of normal reactions in both the cases. This can be solved both from parrot frame and ground frame.

Formula used:
$\eqalign{
  & N - mg = ma \cr
  & N = mg + ma \cr
  & N = W + ma \cr} $

Complete step by step answer:
When cage is not moving let the weight of the cage be W
$W = mg$
Where m is the mass of cage and g is the acceleration due to gravity
Now when cage starts moving up with acceleration ‘a’
Normal reaction N acts upward
Weight W acts downward
Force $m \times a$ acts upward

From ground frame of reference
Balancing the forces gives us
$\eqalign{
  & N - mg = ma \cr
  & N = mg + ma \cr
  & N = W + ma \cr} $
Apparent weight i.e normal reaction is greater than the actual weight and hence parrot feels that the weight of the cage is increased
Hence answer would be option C.

Additional information:
Same question can be solved by the parrot frame of reference. Here pseudo force comes into action. Since parrot-cage system is moving up with acceleration ‘a’ pseudo force will be acting downward and it will be $m \times a$
Upward force = N
Downward forces = $mg + ma$
Equating both the forces we get
$N = W + ma$
Hence both methods will give us the same answer.

Note:
It is to be noted that only weight seems to be increased but not mass. Because mass is always constant wherever we go but weights vary as resultant acceleration varies. A freely falling body feels no weight due to the same property as resultant acceleration would be (g-g =0)
zero. This is called weightlessness. Same applies with the astronaut in the satellite where he feels weightlessness.