Question

A man of mass $60$kg and a boy of mass $30$kg are standing together on frictionless ice surface. If they push each other apart man moves away with a speed of $0.4$m/s relative to ice. After $5$sec they will be away from each other at a distance of.

• A. $9.0$m
• B. $3.0$m
• C. $6.0$m
• D. $30$,

Answer 1

The correct option is C $6.0$m

The man and the boy move in opposite directions.
Momentum of man$=$ momentum of boy
$60\times 0.4=30\times v$
or velocity of the boy $v=0.8m{s}^{-1}$
$\therefore$ Relative velocity $=0.4+0.8=1.2m{s}^{-1}$
$\therefore$ Distance between them in $5$sec $=1.2\times 5=6.0$m.