Calculating Momentum and Velocity in a Football Collision

[pokeefer]

Homework Statement

A 92 kg fullback, running at 5.0 m/s, attempts to dive across the goal line for a touchdown. Just as he reaches the goal line, he is met head-on in midair by two 75 kg linebackers, one moving at 2.0 m/s and the other at 4.0 m/s. If they all become entangled as one mass, with what velocity do they travel? Does the fullback score?

Homework Equations

Momentum = Mass x velocity
P stands for Momentum
Pbefore = Pafter

The Attempt at a Solution

Here is what iv'e done so far. I want to make sure its right.

First I added both of the momentums of the linebackers and then I subtracted that momentum from the fullbacker's momentum to get a difference of 10 kg m/s and then divided that by the total mass of the 3 players combined.

P = M xv
P = Mv1 + Mv2
P = (75)(2) + (75)(4)
P = 150 + 300
P = 450 kg m/s
Pfullback = 92 x 5 = 460 kg m/s
Pchange = 460 kg m/s – 450 kg m/s
Pchange = 10 kg m/s
totalVelocity = totalMomentum/totalMass
Velocity = 10 kg m/s / 242kg
Velocity = 0.041 m/s
Yes the fullback scores.

 

[Gyro]

Good work. Plus I like your enthusiasm for the physics of football.
But how many significant figures should your final answer have?

 

[pokeefer]

I actually don't know how many sig figs. He tells me to watch my sig figs but I just round whenever it seems necessary :p thanks for confirming :)