Question

The vector that must be added to the vector $3 \hat { i } + 6 \hat { j } - 7 \hat { k }$ so that the resultant vector is a unit vector along the y­­-axis is

• A. $4 \hat { i } + 2 \hat { j } + 5 \hat { k }$
• B. $- 4 \hat { i } - 2 \hat { j } + 5 \hat { k }$
• C. $3 \hat { i } + 4 \hat { j } + 5 \hat { k }$
• D. Null vector

Answer 1

Answer: (B)

$- 4 \hat { i } - 2 \hat { j } + 5 \hat { k }$

Answer 2

Unit vector along y axis $= \hat { j }$ so the required vector $= \hat { j } - [ ( \hat { i } - 3 \hat { j } + 2 \hat { k } ) + ( 3 \hat { i } + 6 \hat { j } - 7 \hat { k } ) ]$ $= - 4 \hat { i } - 2 \hat { j } + 5 \hat { k }$