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 particles $A$ and $B$ for their collision is
$\frac{{\overrightarrow {{r_1}} - \overrightarrow {{r_2}} }}{{\left| {\overrightarrow {{r_1}} - \overrightarrow {{r_2}} } \right|}} = \;\frac{{\overrightarrow {{v_2}} - \overrightarrow {{v_1}} }}{{\left| {\overrightarrow {{v_2}} - \overrightarrow {{v_1}} } \right|}}\;\;\;$
$\overrightarrow {{r_1}} $ -$\overrightarrow {{r_2}} $ = $\overrightarrow {{v_1}} $ -$\overrightarrow {{v_2}} $
$\;\overrightarrow {{r_1}} $ .$\;\overrightarrow {{v_1}} $ =$\overrightarrow {{r_2}} $ .$\;\overrightarrow {{v_2}} $
$\;\overrightarrow {{r_1}} \times \overrightarrow {{v_1}}=\overrightarrow {{r_2}} \times \overrightarrow {{v_2}} $
Two cars, both of mass $m$ , collide and stick together. Prior to the collision, one car had been traveling north at speed $2v$ , while the second was traveling at speed $v$ at an angle $\phi $ south of east (as indicated in the figure). The magnitude of the velocity of the two car system immediately after the collision is
A ball hits the floor and rebounds after inelastic collision. In this case
A ball of mass $ m$ moving with velocity $V$, makes a head on elastic collision with a ball of the same mass moving with velocity $2V$ towards it. Taking direction of $V$ as positive velocities of the two balls after collision are
$Assertion$ : In an elastic collision of two billiard balls, the total kinetic energy is conserved during the short time of oscillation of the balls (i.e., when they are in contact).
$Reason$ : Energy spent against friction does not follow the law of conservation of energy.
Consider elastic collision of a particle of mass $m $ moving with a velocity $u$ with another particle of the same mass at rest. After the collision the projectile and the struck particle move in directions making angles ${\theta _1}$and ${\theta _2}$respectively with the initial direction of motion. The sum of the angles. ${\theta _1} + {\theta _2},$ is......$^o$