Final answer:
To come to a complete stop post-collision, the tackle must be moving at 3.33 m/s in the opposite direction before the collision using the conservation of momentum principle.
Step-by-step explanation:
The student's question involves a situation where two players exert forces on each other in a collision and is best analyzed using the principles of conservation of momentum in Physics. According to this principle, the total momentum of a closed system before a collision is equal to the total momentum after the collision, provided no external forces are involved. The collision described is perfectly inelastic because the two players come to a complete stop after colliding, meaning they stick together. To solve for the required speed of the defensive tackle, the momentum of the running back (mass times velocity) must be equal and opposite to the momentum of the tackle. The running back's momentum is 92 kg * 5 m/s = 460 kg*m/s. Setting this equal to the tackle's momentum (138 kg * velocity), and solving for the tackle's velocity, yields 460 kg*m/s / 138 kg = 3.33 m/s. Therefore, the tackle must be moving at 3.33 m/s in the opposite direction before the collision to come to a complete stop post-collision.