Question

Two 72.0-kg hockey players skating at 6.75 m/s collide and stick together.

If the angle between their initial directions was 130 ∘ , what is their speed after the collision?

Answer 1

lets name the players as A and B.

let the direction of motion of A be x axis .

and 90 degree to x axis is y axis.

let unit vector along x axis is i and unit vector along y axis is j.

then initial veloicty of A=6.75 i

initial veloicty of B=6.75*cos(130) i + 6.75*sin(130) j=-4.3388 i + 5.17 j

then initial moment=72*(6.75 i -4.3388 i + 5.17 j)=173.61 i +372.24 j

then using the concept of conservation of momentum,

their speed after collision=initial momentum/final mass

=(173.61 i +372.24 j)/(72+72)

=1.205 i + 2.585 j

then magnitude of velocity=sqrt(1.205^2+2.585^2)=2.852 m/s

hence their final speed will be 2.852 m/s