Physics Momentum and Impulse Practice Momentum Momentum is the resistance of an object to giving up kinetic energy. Momentum is times. 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? [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 of 65Kg. What was his?[2535 kg-m/s] 3. If a 40 Kg object has a 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 of 800Kg*m/s, what is the object s? [40kg] 5. How fast would a ping-pong ball ( 0.0027Kg) have to be traveling to have the same as Scott Macartney just before he fell? 938,888 m/s] 6. A locomotive has a of 200,000 Kg. It is moving at 10 mph (4.5 m/s). How fast would a car ( 1000Kg) be traveling to have the same? [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 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 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- Change When a force is applied for some time to an object that is moving, it will cause the to change. If the of a moving object changes, the changes. This is called the Impulse- change equation: Impulse = change in Ft = m (vf Vi) Thus, a force is required to change the of a moving object! Impulse is just another way to say change. Ft = change and m (vf Vi) is change. In both pictures, the 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 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 of the two objects before the collision is equal to the total of the two objects after the collision. That is, the lost by object 1 is equal to the 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 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 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 equation for collisions Total Momentum before collision = Total after collision m1v1 + m2v2 = m1 v1 + m2 v2 Helpful Information organization chart Collisions Practice Problems 3. Two skate boarders collide while traveling in the same direction. Skate boarder 1 has a of 70 kg and skate boarder 2 has a of 55 kg. What is the speed of skate boarder 2 after the collision? [7.5m/s] 2. Two football players collide head-on. The defensive player has a of 100 kg the offensive player has a 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 2 m/s 1 m/s
3. Two cars collide head on. Car A has a of 1000 kg car B has a of 2000 kg. What is the speed of car B after the collision? [-1m/s] 4. Two cars bump going the same direction. Car A has a of 1000 kg car B has a of 500 kg. What is the speed of car A after the collision? [5m/s]
For Problems 5-8, solve for the unknown quantity. 5. [- 2m/s] 6. [- 10m/s] 7. 8.