Two particles $A$ and $B$, move with constant velocities ${\vec v_1}$ and ${\vec v_2}$. At the initial moment their position vectors are ${\vec r_1}$ and ${\vec r_2}$ respectively. The condition for their collision is
${\vec r_1} - {\vec r_2} = {\vec v_1} - {\vec v_2}$
$\frac{{{{\vec r}_1} - {{\vec r}_2}}}{{\left| {{{\vec r}_1} - {{\vec r}_2}} \right|}} = \frac{{{{\vec v}_2} - {{\vec v}_1}}}{{\left| {{{\vec v}_2} - {{\vec v}_1}} \right|}}$
${{\vec r}_1}.{{\vec v}_1} = {{\vec r}_2}.{{\vec v}_2}$
${{\vec r}_1} \times {{\vec v}_1} = {{\vec r}_2} \times {{\vec v}_2}$
A truck moving on horizontal road towards east with velocity $20\, ms^{-1}$ collides elastically with a light ball moving with velocity $25\, ms^{-1}$ along west. The velocity of the ball just after collision
Four particles $A, B, C$ and $D$ of equal mass are placed at four corners of a square. They move with equal uniform speed $v$ towards the intersection of the diagonals. After collision, $A$ comes to rest, $B$ traces its path back with same speed and $C$ and $D$ move with equal speeds. What is the velocity of $C$ after collision
A spring-block system is resting on a frictionless floor as shown in the figure. The spring constant is $2.0 N m ^{-1}$ and the mass of the block is $2.0 kg$. Ignore the mass of the spring. Initially the spring is in an unstretched condition. Another block of mass $1.0 kg$ moving with a speed of $2.0 m s ^{-1}$ collides elastically with the first block. The collision is such that the $2.0 kg$ block does not hit the wall. The distance, in metres, between the two blocks when the spring returns to its unstretched position for the first time after the collision is. . . . . .
A body of mass $2\,kg$ makes an elastic collision with a second body at rest and continues to move in the original direction but with one fourth of its original speed. What is the mass of the second body? ................ $ \mathrm{kg}$
A body falling from a height of $10\,m$ rebounds from hard floor. If it loses $20\%$ energy in the impact, then coefficient of restitution is