$A$ 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 . . . . . . $J$.

$A$ $50\, g$ bullet moving with velocity $10\, m/s$ strikes a block of mass $950 \,g$ at rest and gets embedded in it. The loss in kinetic energy will be ............... $\%$

$A$ 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 ........

$A$ block of mass $4 m$ travelling at a velocity $v_1$ in the $x$-direction on a frictionless horizontal plane makes a head-on collision with another block of mass $2 m$ travelling in the opposite direction with a velocity $v_2$. After the collision,both blocks travel as a single block along the $x$-direction with a final velocity $5 v_2$. The ratio of velocities $\frac{v_1}{v_2}$ is

$A$ body of mass $m$ moving along a straight line collides with a stationary body of mass $2m$. After collision,if the two bodies move together with the same velocity,then the fraction of kinetic energy lost in the process is

$A$ particle of mass $m$ moving towards west with speed $v$ collides with another particle of mass $m$ moving towards south. If the two particles stick to each other,the speed of the new particle of mass $2m$ will be ..........