Elastic Collision of 89.5kg & 25.5kg Skaters - Kevin & Brother

[spidey12]

Homework Statement

Kevin has a mass of 89.5 kg and is skating with in-line skates. He sees his 25.50 kg younger brother up ahead standing on the sidewalk, with his back turned. Coming up from behind, he grabs his brother and rolls off at a speed of 2.13 m/s. Ignoring friction, find Kevin's speed just before he grabbed his brother.

Homework Equations

1/2m₁v₀₁²+1/2m₂v₀₂²=1/2m₁v_f1²+1/2m₂v_f2²

The Attempt at a Solution

I have tried many ways of doing this problem, and I keep arriving at the same answer: 2.41 m/s which is incorrect. I then decided to pretend that the kid and his brother are one unit so i added their masses together multiplied times the 2.13² divided by 2 and set that equal to the left side of the above equation. However i again got 2.41. It seems that every way i try this problem i get 2.41

What am i doing wrong?

 

[LowlyPion]

Homework Statement

Kevin has a mass of 89.5 kg and is skating with in-line skates. He sees his 25.50 kg younger brother up ahead standing on the sidewalk, with his back turned. Coming up from behind, he grabs his brother and rolls off at a speed of 2.13 m/s. Ignoring friction, find Kevin's speed just before he grabbed his brother.

Homework Equations

1/2m₁v₀₁²+1/2m₂v₀₂²=1/2m₁v_f1²+1/2m₂v_f2²

The Attempt at a Solution

I have tried many ways of doing this problem, and I keep arriving at the same answer: 2.41 m/s which is incorrect. I then decided to pretend that the kid and his brother are one unit so i added their masses together multiplied times the 2.13² divided by 2 and set that equal to the left side of the above equation. However i again got 2.41. It seems that every way i try this problem i get 2.41

What am i doing wrong?

Aren't you supposed to be conserving momentum? Isn't that simply m x v ?

 

[spidey12]

Aren't you supposed to be conserving linear momentum? Isn't that simply m x v ?

I am an idiot. I read waaaay to much into this problem. I got it. Thank you.