A particle of mass m moving with a speed v along the x-axis, collides with another particle of the same mass m moving with the same speed v along the y-axis. After collision, the two particles coalesce. What is the magnitude and the direction of the velocity of the composite particle?


Correct option is


AB = p1 is the momentum vector of the first particle and CB = p2 that of the second particle. Vector CB is shifted parallel to itself to a position BDso that the tail of BD is at the arrow head of AB. From the triangle law of vector addition, the resultant momentum P is given by vector AD.   

The magnitude of the resultant is given by