A 84 kg runningback is running at 3.5 m/s. The running back is met by 152 kg defensive lineman. If the collision between the runningback and the defensive lineman results in both coming to a stop, find the speed(absolute value) that the defensive lineman was moving at.

so far no one is answering our questions. you should try conservation of momentum: m1v1 + m2v2=(m1+m2)vf then just solve for vf, your final velocity...just a suggestion in case you haven't tried it yet.

actually i think that's wrong, i think its only when they collide and one pushes the other. as result they move in the same direction

To find the speed at which the defensive lineman was moving, we can use the principle of conservation of momentum. According to this principle, the total momentum before the collision is equal to the total momentum after the collision.

Momentum (p) is defined as the product of an object's mass (m) and its velocity (v):

p = m * v

Let's denote the mass of the running back as m1, the mass of the defensive lineman as m2, the initial velocity of the running back as v1, and the initial velocity of the defensive lineman as v2. After the collision, both players come to a stop, so their final velocities are 0.

Using the principle of conservation of momentum, we can set up the equation:

m1 * v1 + m2 * v2 = 0

Plugging in the known values:

(84 kg) * (3.5 m/s) + (152 kg) * v2 = 0

Now, solve for v2:

(84 kg * 3.5 m/s) = - (152 kg * v2)

294 kg*m/s = -152 kg * v2

v2 = - (294 kg*m/s) / (152 kg)

v2 ≈ -1.934 m/s

Since speed is always a positive value, we take the absolute value:

|v2| ≈ 1.934 m/s

Therefore, the speed at which the defensive lineman was moving is approximately 1.934 m/s.