Conservation of Momentum

A sharp object of mass $0.5 \mathrm{kg}$ travelling horizontally at a velocity of $100 {\mathrm{ms}}^{-1}$ strikes a stationary wooden block of mass $2.5 \mathrm{kg}$. Therefore, the two move together in the same straight line. Calculate the total momentum before and after the impact. Also, calculate the velocity of the combined system.

Two bodies having each of mass $2 \mathrm{kg}$ are moving in the same straight line but in opposite directions. The velocity of each before collision is $3 {\mathrm{ms}}^{-1}$. In the collision, they stick together. What will be the velocity of the combined body after collision?