# Q 15.     An object of mass 1 kg travelling in a straight line with a velocity of 10 m s-1 collides with, and sticks to, a stationary wooden block of mass 5 kg. Then they both move off together in the same straight line. Calculate the total momentum just before the impact and just after the impact. Also, calculate the velocity of the combined object.

For calculating the velocity of the combined mass we need to use the law of conservation of momentum.

$m_1u_1\ +\ m_2u_2\ =\ (m_1\ +\ m_2)v$

or                                                         $1\times 10\ +\ 5\times 0\ =\ (1\ +\ 5)v$

or                                                                                        $v\ =\ \frac{10}{6}$

or                                                                                        $v\ =\ 1.66\ m/s$

Now, the momentum before the collision is :

$p_i\ =\ m_1u_1\ +\ m_2u_2$

or                                                       $=\ 1\times 10\ +\ 5\times 0\ =\ 10\ Kg\ m/s$

By momentum conservation, final momentum is also    $10\ Kg\ m/s$

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