Physics
Momentum and Impulse Practice
Momentum Momentum is the resistance of an object to
giving up kinetic energy. Momentum is mass
times velocity. It is abbreviated with a “p”. The equation is
p = m*v
Solve the following problems in the space provided. Write the equation first, substitute in the
numbers and then solve:
1. A 100Kg man is running at 5.6m/s. What is his momentum? [560kg-m/s]
2. Scott Macartney, a US Olympic Ski Team member was going 88 miles per hour (39 m/s) in the
downhill ski race when lost his balance and fell. He has a mass of 65Kg. What was his
momentum?[2535 kg-m/s]
3. If a 40 Kg object has a momentum of 400Kg*m/s, how fast is it traveling?[10m/s]
4. If an object traveling at 20 m/s (about 44 miles per hour) has a momentum of 800Kg*m/s, what is
the object’s mass? [40kg]
5. How fast would a ping-pong ball (mass 0.0027Kg) have to be traveling to have the same
momentum as Scott Macartney just before he fell? 938,888 m/s]
6. A locomotive has a mass of 200,000 Kg. It is moving at 10 mph (4.5 m/s). How fast would a car
(mass 1000Kg) be traveling to have the same momentum? [900m/s]
7. In a sentence or two, describe what would happen if the car and locomotive in #6 above ran head
on into each other. [transfer all the momentum to the other object]
Impulse 8. If you can run 15 miles per hour (6.7 m/s) while holding a 8 pound (3.5 Kg) shot put, how much
momentum does the shot put have? [23.45 kg-m/s]
Impulse is when a force is applied to a moving object. Impulse is abbreviated as “J”. J = F x t 9. A football player kicks a ball with a force of 50N. Find the impulse on the ball if his foot stays in
contact with the football for 0.01s. [0.5Ns]
10. A hockey player applies an average force of 80N to a 0.25kg hockey puck for a time of 0.2s.
Determine the impulse experienced by the hockey puck. [16Ns]
11. Aunt Mary needs to hang a picture in her bedroom. She uses a hammer to drive the nail into the
wall. Find the force exerted by the hammer on the nail if the hammer stays in contact with the
nail for 0.5s and has an impulse of 25Ns. [50N]
Impulse-­‐momentum Change When a force is applied for some time to an object that is moving, it will cause the velocity to change. If the velocity of a moving object changes, the momentum changes. This is called the Impulse-­‐momentum change equation: Impulse = change in momentum Ft = m (vf – Vi) Thus, a force is required to change the velocity of a moving object! Impulse is just another way to say momentum change. Ft = momentum change and m (vf – Vi) is momentum change. In both pictures, the momentum change (or impulse) is the same. In both pictures the boxer was stopped by applying a force over a period of time. It just so happens, that in the picture on the left, the boxer “rode with” the punch, increasing the time of impact, thus reducing the force. But the impulse on the left, was the same as him leaning into the punch; where time was decreased thus increasing the force. 12. What is the symbol for impulse? [J]
13. How much impulse is needed to stop a 10-kg bowling ball moving at 6 m/s? [-60Ns or -60kgm/s]
14. A car with a mass of 1000 kg moves at 20 m/s. What is the the braking force needed to bring the
car to a halt in 10s? [2000 N]
15. A car carrying a 75-kg test dummy crashes into a wall at 25 m/s and is brought to rest in 0.1 s.
What is the average force exerted by the seat belt on the dummy? [18,750 N]
The Law of Conservation of Momentum The Law of Conservation of Momentum
states: For a collision the total momentum
of the two objects before the collision is
equal to the total momentum of the two
objects after the collision. That is, the
momentum lost by object 1 is equal to the
momentum gained by object 2.
Conservation of Momentum and Kinetic Energy Momentum is conserved for any isolated collision, but kinetic energy is
usually not. Kinetic energy can be converted into thermal energy and
internal elastic potential energy (because of deformations).
Inelastic Collisions An inelastic collision is one in which part of the kinetic energy is changed
to some other form of energy in the collision. Thus momentum is
conserved but the kinetic energy is not. This is when two or more objects
hit and stick together.
A large object striking a very small object
at rest will lose very little of its kinetic
energy. If your car strikes an insect, it is
unfortunate for the insect but will not
appreciably slow your car. On the other
hand, if a small object collides inelastically
with a large one, it will lose most of its kinetic energy.
Perfectly inelastic collision
Perfectly inelastic collisions are when the
two objects stick together after the
collision. In perfectly inelastic collisions
the momentum of the system is conserved
but there is a change in the kinetic energy
of the system.
Perfectly Elastic collision (Perfect Rebound) Perfectly elastic collisions are those in which no kinetic energy
is lost in the collision.
Conservation of momentum equation for collisions Total Momentum before collision = Total momentum after collision m1v1 + m2v2 = m1’v1’ + m2’v2’ Helpful Information organization chart
Before collision After Collision Object 1 Object 2 Object 1 Object 2 mass velocity momentum Collisions Practice Problems 3. Two skate boarders collide while traveling in the same direction. Skate boarder 1
has a mass of 70 kg and skate boarder 2 has a mass of 55 kg. What is the
speed of skate boarder 2 after the collision? [7.5m/s]
mass velocity momentum Before collision Object 1 Object 2 After Collision Object 1 Object 2 2. Two football players collide head-on. The defensive player has a mass of 100 kg
the offensive player has a mass of 90 kg. What is the speed of the offensive player
after the collision? [3.6m/s]
(defense) (offense)
(defense)
100 kg------> <--------90 kg
100 kg-->
6 m/s
1 m/s
mass velocity momentum 2 m/s
Before collision Object 1 Object 2 After Collision Object 1 Object 2 3. Two cars collide head on. Car A has a mass of 1000 kg car B has a mass of
2000 kg. What is the speed of car B after the collision? [-1m/s]
mass velocity momentum Before collision Object 1 Object 2 After Collision Object 1 Object 2 4. Two cars bump going the same direction. Car A has a mass of 1000 kg car B has
a mass of 500 kg. What is the speed of car A after the collision? [5m/s]
mass velocity momentum Before collision Object 1 Object 2 After Collision Object 1 Object 2 For Problems 5-­‐8, solve for the unknown quantity. 5. [-­‐2m/s]
6. [-­‐10m/s] 7. 8.