Answer: 0.35 m/s to the right.
Explanation:
Let's define M1 and V1 as the mass and velocity of the linebacker, and define the right as the positive side.
M1 = 125kg
V1 = 2.5m/s
M2 and V2 as the velocity and mass of the quarterback.
M2 = 80kg
V2 = -3m/s
where V2 has a minus sign because the quarterback is running to the left.
We know that after the collision, both players keep stick togheter, so we can think this as an perfectly inleastic collision, where the velocity of both players can be obtained by:
v = (M1*V1 + M2*V2)/(M1 + M2) = (125kg*2.5m/s - 80kg*3m/s)/(125kg + 80kg)
v = (72.5/205) m/s = 0.35m/s
Because this velocity is positive, this means that both players are moving to the right.
