$A$ bullet strikes a solid block resting on a frictionless horizontal table and gets embedded in it. Which of the following is conserved?

$A$ particle of mass $m$ moving with velocity $v$ collides with a stationary particle of mass $2m$. After collision,they stick together and continue to move together with velocity ........

$A$ bullet strikes against a wooden block and is embedded in it,the nature of collision is

Two bodies of the same mass $m$ are moving with the same speed $v_0$,but in different directions in a plane. They undergo a completely inelastic collision and move together thereafter with a final speed which is half of their initial speed. The angle between the initial velocities of the two bodies (in degrees) is:

$A$ body of mass $20 \ kg$ moving with a velocity of $10 \ m/s$ collides with a stationary body of mass $5 \ kg$ and sticks to it. The combined kinetic energy of the system after the collision is . . . . . . $J$.

An object of mass $80 \,kg$ moving with velocity $2 \,ms^{-1}$ collides with another object of mass $20 \,kg$ moving with velocity $4 \,ms^{-1}$. Find the loss of energy assuming a perfectly inelastic collision. ........... $J$