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Momentum

? – If a bowling ball and tennis ball were rolled down a bowling alley at the same speed, which would knock more pins down? Why?

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Momentum

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  1. ? – If a bowling ball and tennis ball were rolled down a bowling alley at the same speed, which would knock more pins down? Why? ? – What if two 8 lb bowling balls were rolled down the alley, but a 7 yr old rolled one ball while an adult rolled the other. Which one would knock know the most pins? Why?

  2. Momentum • Based upon mass and speed • Vector • Represented by the letter “p” • To calculate – p = mv • Units – kg*m/s

  3. Practice • An ostrich with a mass of 146 kg is running to the right with a velocity of 17 m/s What is the ostrich’s momentum? • A 21 kg child is riding a 5.9 kg bike with a velocity of 4.5 m/s to the northwest. What is the total momentum of the child and bike? • What velocity must a car with a mass of 1210 kg have in order to have a momentum of 56250 kg*m/s?

  4. An ostrich with a mass of 146 kg is running to the right with a velocity of 17 m/s What is the ostrich’s momentum? • P = mv • P = (146)(17) • P = 2482 kg*m/s, right

  5. A 21 kg child is riding a 5.9 kg bike with a velocity of 4.5 m/s to the northwest. What is the total momentum of the child and bike? • P = mv • P = (21+5.9)(4.5) • P = 121.05 kg*m/s, northwest

  6. What velocity must a car with a mass of 1210 kg have in order to have a momentum of 56250 kg*m/s? • P = mv • 56250 = 1210(v) • V = 46.48 m/s, in the direction the car is moving

  7. ? – What do you have to do in order to change the momentum of an object? ? – Does an objects motion change instantly? The change in momentum occurs when a force is applied over a certain amount of time = IMPULSE p = Ft mv = Ft

  8. Practice • A 0.50 kg football is thrown with a velocity of 15 m/s to the right. A stationary receiver catches the ball and brings it to rest in 0.020 s. What is the force exerted on the receiver? • An 82 kg man drops from rest on a diving board 3.0 m above the surface of the water and comes to rest 0.55 s after reaching the water. What force does the water exert on him? • A 0.40 kg soccer ball approaches a player horizontally with a velocity of 18 m/s to the north. The player strikes the ball and causes it to move in the opposite direction with a velocity of 22 m/s. What impulse was delivered to the ball by the player? • A 2250 kg car traveling to the west slows down uniformly from 20.0 m/s to 5.0 m/s. How long does it take the car to decelerate if the force on the car is 8450 N to the east? How far does the car travel during the deceleration?

  9. A 0.50 kg football is thrown with a velocity of 15 m/s to the right. A stationary receiver catches the ball and brings it to rest in 0.020 s. What is the force exerted on the receiver? • mv = Ft • 0.50 (0-15) = F (0.20) • -37.5 N (left)

  10. An 82 kg man drops from rest on a diving board 3.0 m above the surface of the water and comes to rest 0.55 s after reaching the water. What force does the water exert on him? • mv = Ft vf2 = vi2 + 2ax • 82(7.67-0) = F(.55) vf2 = 0 + 2(9.8)(3) • F = 1143.2 N upvf = 7.67 m/s

  11. A 0.40 kg soccer ball approaches a player horizontally with a velocity of 18 m/s to the north. The player strikes the ball and causes it to move in the opposite direction with a velocity of 22 m/s. What impulse was delivered to the ball by the player? • mv = Ft • 0.4(-22-18) = Ft • -16 kg*m/s

  12. A 2250 kg car traveling to the west slows down uniformly from 20.0 m/s to 5.0 m/s. How long does it take the car to decelerate if the force on the car is 8450 N to the east? How far does the car travel during the deceleration? • mv = Ft • 2250(-5-(-20)) = 8450(t) • t = 3.99 s

  13. Collisions Elastic vs. Inelastic Object hit and bounce off each other Objects hit and stick together • Total mass after collision is • the combination of the • two objects • Kinetic Energy is not conserved • Velocities are the same • Masses stay separate • Kinetic energy is conversed • Velocities are different Law of Conservation of Momentum The momentum before a collision and after a collision is the same

  14. Examples • A 1850 kg luxury sedan stopped at a traffic light is struck from the rear by a compact car with a mass of 975 kg. The two cars become entangled as a result of the collision. If the compact car was moving at a velocity of 22.0 m/s to the north before the collision, what is the velocity of the entangled mass after the collision? • A 0.015 kg marble moving to the right at 0.225 m/s makes an elastic head on collision with a 0.030 kg shooter marble moving to the left at 0.180 m/s. After the collision, the smaller marble moves to the left at 0.315 m/s. Assume that neither marble rotates before or after the collision and that both marbles are moving on a frictionless surface. What is the velocity of the 0.030 kg marble after the collision?

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