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## Homework Statement

A collision occurs between two football players. Player 1 has mass of 75 kg and a velocity of 6 m/s. Player 2 has mass of 150 kg and a velocity of -3 m/s (meaning going in an opposite direction). Assuming an ELASTIC collision, what is the final velocity of player 2?

## Homework Equations

They gave us this equation in class to calculate the final velocity:

m = mass

Vi = initial velocity

Vf = final velocity

a = player 1

b = player 2

Vfb = [(2*ma)/(ma+mb)]*Via + [(mb-ma)/(ma+mb)]*Vib

## The Attempt at a Solution

Using the equation above and plugging in the numbers:

Vfb =

[(2*75kg)/(75kg + 150kg)]*(6 m/s)

+

[(150kg - 75kg)/(75kg + 150kg)]*(-3 m/s)

which gives me:

Vfb = 4 m/s + -1 m/s = 3 m/s

The "online" homework solution says it is -3 m/s. Am I incorrect? Did I miss a negative sign somewhere, or is there a principle of momentum that I am not getting?