# Relativistic momentum football problem

## Homework Statement

A football player with a mass of 82.1 kg and a speed of 2.00 m/s collides head-on with a player from the opposing team whose mass is 126 kg. The players stick together and are at rest after the collision. Calculate the speed of the second player, assuming the speed of light is 3.00 m/s

## Homework Equations

p= mv/[sqrt(1-v^2/c^2)]

## The Attempt at a Solution

Basically how i attempted to solve this is used the above equation for each player, and set them equal to each other using 3.00m/s as the speed of light, because if they are at rest after the collision then their momentum must be equal. Because i have knowns for 1 player, and the mass of the other player, I should be able to solve for v, the other players speed, but the answer i calculate isn't right.... any suggestions?

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diazona
Homework Helper
First suggestion: show your work in more detail... I don't notice any obvious issues but maybe if you actually specify what you did something will become clear.

p= 82.1*2/[sqrt(1-2^2/3^2)]
p= 220.297

220.297=126*v/[sqrt(1-(v^2/3^2)]
v= 1.94m/s which is not correct

p= 82.1*2/[sqrt(1-2^2/3^2)]
p= 220.297

220.297=126*v/[sqrt(1-(v^2/3^2)]
v= 1.94m/s which is not correct