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## Momentum

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**Learning Tweet**• Units of momentum (change in momentum) = kgm/s • Change in momentum depends on the size of the force and the time it acts • Change in momentum = resultant force (N) x time (s)**Unscramble the words & make two sentences**• NCEDSTI • EMIT • ELVICYT • HAGPR • EPEDS • CELECATNIOAR**DISTANCE**• TIME • VELOCITY • GRAPH • SPEED • ACCELERATION**Momentum answers 1**A – football = 12.5 kg m/s Tennis ball leaving racquet = 3kg m/s Golf ball = 2.05 kg m/s B Car = 22000 kg m/s Lorry = 130 000 kg m/s Van = 77500 kg m/s C sprinter = 500 kg m/s Dog = 120 kg m/s Cyclist = 910 kg m/s**Momentum answers 2**1 a 5000 kg m/s b 31 600 kg m/s c720 000 kg m/s d 480 000kg m/s • 1.8 x1029 kg m/s • 31.6 m/s (about 70 mph )**Momentum answers 3**1 A 23000 kg m/s B - 5400 kg m/s 2 A 9 kg m/s B -9kg m/s C 18 kg m/s**Change in momentum**• Momentum = Mass x velocity • Force x time (during which the force acts) = change in momentum**Problems**• A snooker cue hits a ball. • The ball has a mass of 0.17 kg and starts moving with a velocity of 1.4m/s. • A What is the momentum of the ball • Momentum = 0.17 x 1.4 = 0.238 kg m/s • B The contact between the cue and the ball lasts for 0.1s. What is the average force exerted on the cue ball during this time? • F x t = change in momentum • F= change in mom/time = 0.238/0.1 = 2.38 N**Problems (2)**• A motorcycle with a mass 200kg has a rider with a mass 50kg. It is travelling at 27 m/s (60 mph) • a What is the momentum of motorcycle & rider • b What braking force is needed to bring the motorcycle and rider to stop in 5s?**Problems (3)**• A car (mass 1025kg) has collided with a brick wall. It was travelling at 23m/s(50mph) • What was the momentum of the car • The accident investigator estimated that it took 1.8s to stop. What average force was exerted on the car during the collision.