Question

The velocity of a boat with respect to ground is 3i + 4j and the velocity of water with respect to ground is -3i - 4j. Hence the velocity of boat with respect to water is ........... .
(A) 8i
(B) -6i - 8j
(C) 6i + 8j
(D) 6i

Answer 1

Answer:

Velocity of boat with respect to water = $6i+8j$

Explanation:

$\vec{V}_{bg}$ = velocity of boat w.r.t ground = 3i+4j

$\vec{V}_{wg}$ = velocity of water w.r.t ground = -3i-4j

$\vec{V}_{bw}$ = velocity of boat w.r.t water.

Now according to concept of relative velocity,

$\vec{V}_{bw} = \vec{V}_{bg} - \vec{V}_{wg}$

$\vec{V}_{bw} = (3i+4j)-(-3i-4j)$

$\vec{V}_{bw} = 6i+8j$  

Option (C) is correct.