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ESPN Movie – Running with Momentum
1. What is it called when two objects come together?
A collision
2. What must you have in order for a collision to take place?
momentum
3. How can a smaller player have enough momentum to push back a giant defender?
He might have less mass but he can get up to a greater speed (in less time)
4. What is linear momentum?
Anything that is moving in a straight line will have mass and velocity in this direction
5. A quantity of motion is what?
momentum
6. What does it take to change your momentum?
An outside force
7. Momentum depends on what two things? What are they?
Mass (inertia) and velocity
8. What is the equation for momentum?
P = m v
9. What does conservation of momentum mean exactly?
If there are no outside forces acting on an object its momentum will stay the same. The momentum will just keep
on going and going. Friction is an outside force that will change the momentum of an object.
10. After a collision of two objects what happens to the momentum?
The total momentum will stay the same
11. After a “sticky collision” where Napoleon is tackled at right angles to his initial motion, why
does he feel like he has lost momentum?
Because he has lost speed because he has effectively gained mass (……the other player’s that is!)
12. What will friction (outside force) do to the momentum in a system?
It will reduce it
13. Is momentum a vector or a scalar quantity? How do you represent it on paper?
It is a vector quantity. You represent it with vector arrows.
14. What is the total momenta of two linemen with the same mass and speed moving towards
each other? Explain what will happen when they collide!
They have the same momenta but in opposite directions before they collided
So the total momenta was zero before they collided (0 = p + -p)
It still must be zero after the collision so they must stop (or bounce back with the same speed).
15. What happens to the total momenta when two objects collide at an angle to each other?
It stays the same as before the collision according to the conservation law
16. A 130 kg defender moving forwards at 9 m/s tackles a 84kg running back moving towards
him at 6 m/s. If a sticky collision takes place what velocity (speed and Direction) do the
players move off at after the collision?
mD vD I + mB vB I
=
(mD + mB) vf
(130kg)(9m/s) + (84kg)(-6m/s) = (130kg + 84kg) vf
+666 kgm/s
=
+3.12 m/s
=
214 kg vf
vf
(answer is positive so they must move forwards)
17. A 130 kg defender moving forwards at 9 m/s tackles a 84kg running back moving
sideways at 6 m/s. If a sticky collision takes place what velocity (speed and Direction) do
the players move off at after the collision? – Draw a scale diagram to solve this problem!
pB i
= MB vB I
= (84kg) (6m/s) = 504 kgm/s
pD I = mD vD I
pf =  (pB i2 + pD i2)
(130kg) (9m/s)
p f =  ( 504 kgm/s2 + 1170 kgm/s 2) = 1273.9 kgm/s
1170 kgm/s
vf = pf / (mB + mD) = 1273.9 kgm/s / 214kg = 5.95 m/s

 = tan-1 (pB i / pD I ) = tan-1 (504 / 1170) = 23.30