Question

A fish, $F$ in the pond is at a depth of $0.8\, m$ from water surface and is moving vertically upwards with velocity $2 \, ms^{-1}$. At the same instant a bird $B$ is at a height of $6 \, m$ from water surface and is moving downwards with velocity $3 \, m s^{-1}$. At this instant both are on the same vertical line as shown in Fig. Which of the following statements is/are correct?

• A. Height of $B$, observed by $F$ (from itself) is equal to $5.30\, m$.
• B. Depth of $F$, observed by $B$ (from itself) is equal to $6.60\, m$.
• C. Height of $B$, observed by $F$ (from itself) is equal to $8.05\, m$.
• D. Depth of $F$, observed by $B$ (from itself) is equal to $8.8 \, m$.

Answer 1

Answer: (B)

(a) For the fish, the bird appears at a height of $\frac{6}{3 / 4}=\frac{6 \times 4}{3}=8\, m$ from water surface
(b) For the bird, the fish appears at a depth of $\frac{0.8}{4 / 3}=\frac{0.8 \times 3}{4}=0.6 \,m$ below water surface
Hence the bird sees the fish $6.60 \,m$ away while the fish sees the bird $8.8\, m$ away