# Two masses of $0.1\;kg$ and $0.4 \;kg$ move towards each other with velocities $1 m/s$ and $0.1 m/s$ respectively. After collision they stick together . In 10 seconds the combined mass travels

$(a)\;120\;m \quad (b)\;0.12\;m\quad (c)\; 12 \;m \quad (d)\;1.2\;m$

Velocity of combined mass
$v=\large\frac{m_1v_1-m_2v_2}{m_1+m_2}$
$\quad= \large\frac{0.1 \times 1 - 0.4 \times 0.1}{0.1+0.4}$
$\quad= 0.12 m$
distance traveled in 10 s
$\quad=0.12 \times 10$
$\quad=1.2 \;m$
Hence d is the correct answer.

edited Feb 17, 2014 by meena.p