Question

An old man and a boy are walking towards each other and a bird is flying over them as shown in the figure.
Find the velocity of tree, bird and old man as seen by boy respectively.

• A. $-16\hat{i},12\hat{j},-18\hat{i}$
• B. $16\hat{i},-12\hat{j},18\hat{i}$
• C. $16\hat{i},12\hat{j},18\hat{i}$
• D. $16\hat{i},-12\hat{j},20\hat{i}$

Answer 1

The correct option is A $-16\hat{i},12\hat{j},-18\hat{i}$

Velocity of boy with respect to ground, $v_B=16\hat{i}$
Velocity of tree w.r.t ground, $v_t=0$
Velocity of tree with respect to boy, $v_{tB}=v_t-v_B=0-16\hat{i}=-16\hat{i}$
Velocity of bird with respect to ground, $v_b=16\hat{i}+12\hat{j}$
Velocity of bird with respect to boy is, $v_{bB}=v_b-v_B=16\hat{i}+12\hat{j}-16\hat{i}=12\hat{j}$
Velocity of old man with respect to ground, $v_o=-2\hat{i}$
Velocity of old man with respect to boy, $v_{ob}=v_o-v_B=-2\hat{i}-16\hat{i}=-18\hat{j}$