Question

Two particles of equal masses moving with same speed collide perfectly inelastically. After the collision the combined mass moves with half of the speed of the individual masses. The angle between the initial momenta of individual particle is :

• A. ${60}^o$
• B. ${90}^o$
• C. ${120}^o$
• D. ${45}^o$

Answer 1

The correct option is C ${120}^o$

Conservation of linear momentum in $x-$direction

$mv\cos \varphi +mv\cos \varphi =2m\times \frac{v}{2}$

$2mv\cos \varphi =mv$

or $\cos \varphi =\frac{1}{2}$

$\varphi =60°$

$\therefore \varphi =120°[2\varphi =\theta ]$