In perfectly inelastic collisions,the relative velocity of the bodies

$A$ body of mass $m$ moving with velocity $v$ collides head-on with another body of mass $2m$ which is initially at rest. If the collision is perfectly inelastic,what is the loss in kinetic energy of the system?

$A$ metal ball of mass $2 \ kg$ moves with a speed of $36 \ km/hr$. It collides with a stationary ball of mass $3 \ kg$. If both balls move together after the collision,the loss in kinetic energy due to the collision is ........... $J$.

$A$ metal ball of mass $2 \,kg$ moving with a velocity of $36 \,km/h$ has a head-on collision with a stationary ball of mass $3 \,kg$. If after the collision,the two balls move together,the loss in kinetic energy due to the collision is ........ $J$.

$A$ scooter of mass $40 \ kg$ moving with a velocity of $4 \ m/s$ collides with another scooter of mass $60 \ kg$ moving with a velocity of $2 \ m/s$. After the collision,both scooters stick together. Find the loss in kinetic energy in $J$.

$A$ body of mass $1 \ g$ moving with a velocity of $3\hat{i} - 2\hat{j} \ m/s$ collides with a body of mass $2 \ g$ moving with a velocity of $4\hat{j} - 6\hat{k} \ m/s$. If the two bodies stick together after the collision,what is the magnitude of their combined velocity in $m/s$?