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

$A$ bullet of mass $m$ moving with a speed $v$ strikes a wooden block of mass $M$ and gets embedded into the block. The final speed is

$A$ body of mass $2 \ kg$ is moving with a velocity of $36 \ km/h$. It collides inelastically with a stationary body of mass $3 \ kg$. The loss in kinetic energy is ..... $J$.

$A$ metal ball of mass $2 \,kg$ moving with a speed of $10 \,ms^{-1}$ has a head-on collision with a stationary ball of mass $3 \,kg$. If after the collision, both the balls move together, then the loss in kinetic energy due to the collision is: (in $\,J.$)

$A$ bag (mass $M$) hangs by a long thread and a bullet (mass $m$) comes horizontally with velocity $v$ and gets caught in the bag. Then for the combined (bag $+$ bullet) system

$A$ bag of sand of mass $9.8 \, kg$ is suspended by a rope. $A$ bullet of mass $200 \, g$ travelling with a speed of $10 \, ms^{-1}$ gets embedded in it. The loss of kinetic energy will be $... J$.