Question

A bird is sitting on the floor of a closed glass cage in the hands of girls. Will the girl experience any change in the weight of the cage when the bird (i) starts flying in the cage with a constant velocity ? (ii) flies upwards with acceleration ? (iii) flies downwards with acceleration?

Answer 1

Step 1:

1. In the hands of two girls, a bird sits on the floor of a closed glass cage. Will the girl notice any difference in the weight of the cage when the bird arrives?

Step 2:

1. When the bird starts flying with constant velocity then acceleration is zero, there is no change in the weight of the cage.
2. When the bird flies up with acceleration (say $a$)
   $\therefore$ Reaction $\mathrm{R}$ is
   $$\begin{gathered} \mathrm{R}-\mathrm{Mg}=\mathrm{M}a \\ \therefore \mathrm{R}=\mathrm{M}g+\mathrm{M}a=\mathrm{M}(g+a) \end{gathered}$$
   Thus the cage will appear heavier than before
3. When a bird flies downward with acceleration $\mathit{a}$
   $\begin{array}{l}\therefore \mathrm{Mg}-\mathrm{R}=\mathrm{Ma}\\ \mathrm{R}=\mathrm{Mg}-\mathrm{Ma}=\mathrm{M}(\mathrm{g}-a)\end{array}$
   $\therefore$ The cage will appear lighter than earlier.