Question

Find the velocity of the boy as seen by bird.

• A. $-12\hat{j}$
• B. $12\hat{j}$
• C. $12\hat{k}$
• D. $10\hat{i}-12\hat{j}$

Answer 1

Answer: (A)

$-12\hat{j}$

With respect to Bird :
$v_{True}=12m/s(\downarrow )$ and $16m/s(\leftarrow )$ or $-{12}_{\hat{j}}+{16}_{\hat{i}}$
$v_{oldman}=18m/s(\leftarrow )$ and $12m/s(\downarrow )$ $-{18}_{\hat{i}}-{12}_{\hat{j}}$
$v_{Boy}=12m/s(\downarrow )$ or $-12\hat{j}$

here we have to find the velocity of boy w.r.t bird
hence we see that $(V_x$ for bird $=16m/sec$)
$(V_y$ for bird $=12m/sec$)
horizontal velocity of boy$(V_x$ for boy$=16m/sec$)
vertical component of boy$(V_y$ for boy$=0$)
so horizontal velocity of boy with respect to bird will be $(V_x$ $=16$$\hat{i}$$-16$$\hat{i}$$=0$
vertical velocity of boy with respect to bird will be $V_y$ $=0-12$$\hat{j}$