A 70 kg football player running at 3m/s north tackles an 80kg player running at 1.5 m/s south. what is the magnitude and direction of the entangled players after the collision?

a).6 m/s north

b) 2.2 m/s north

c).6 m/s south

d) 2.2 m/s south

It could never actually happen like this, but the question is

looking for you to 'conserve' the momentum.

Momentum of a moving object is (mass) x (velocity).

Like velocity, momentum has a direction.

Momentum is one of those things that's 'conserved'.

That means that momentum can't appear out of nowhere, and

it doesn't disappear. The total after the collision is the same as

the total was before the collision.

Momentum of the skinny player:

(70 kg) x (3 m/s north) = 210 kg-m/s north.

Momentum of the heavy player:

(80 kg) x (1.5 m/s south) = 120 kg-m/s south.

Total momentum before the collision is

(210 kg-m/s north) + (120 kg-m/s south)

= 90 kg-m/s north.

It has to be the same after the collision.

(mass) x (velocity) = 90 kg-m/s north.

The mass after the collision is 150 kg, because they get

tangled up and stuck together, and they move together.

(150 kg) x (velocity) = 90 kg-m/s north.

Divide each side

by 150 kg : velocity = (90 kg-m/s north) / (150 kg)

= (90/150) (kg-m/s / kg north)

= 0.6 m/s north.