Question

A person is moving with a velocity of $10\, ms ^{-1}$ towards north. A car moving with a velocity of $20\, ms ^{-1}$ towards south crosses the person. The velocity of car relative to the person is

• A. $-30 \,ms ^{-1}$
• B. $+20 \,ms ^{-1}$
• C. $10 \,ms ^{-1}$
• D. $-10 \,ms ^{-1}$

Answer 1

Answer: (A)

Let south to north direction be positive.
Velocity of car, $v_{C}=-20 \,ms ^{-1}$
Velocity of person, $v_{P}=+10 \,ms ^{-1}$
$v_{C P} =v_{C}-v_{P} $
$=(-20)-(10)$
$=-30\, ms ^{-1}$