Question

What is kinetic energy after collision of mass 4kg moving 6m/s in +y direction collids and stick to another object with mass 2kg moving at 4m/s in +x direction.

Answer 1

First apply conservation of momentum to get the final velocity V of the stuck-together masses. It will have both x and y components

The x-component of the final velocity is Vx = 2*4/(M1+M2) = 8/6 = 1.333 m/s

The y-component of the final velocity is
Vy = 4*6/(M1+M2) = 42/6 = 4.000 m/s

The final KE is (1/2)(M1+M2)V^2
= (1/2)(M1+M2)(Vx^2 + Vy^2)
= 53.33 J

(Note that the initial KE was 72 + 16 = 88 J)