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Linear Momentum Physics Mrs. Coyle Linear Momentum, p p= m v • Momentum is a vector. • The direction of momentum is the same as the direction of the velocity of the object. • Unit: kg m/s or N s • “Inertia in Motion” Question 1: • What has more momentum, a dump truck at rest or a pebble moving down a hill at 1m/s? Question 2 • How can you change the momentum of an object? Impulse = Impulse = p = m v = Ft Problem 1 • Starting with Newton’s second law, show that for a constant force, p = m v = Ft . For a given change in velocity, p is constant : To reduce the force of impact, increase the time of impact. Question 3: • How do you have a better chance of winning in a water balloon toss contest? Question 4: • Why does a boxer “roll with the punches”? Question 5: • Why should you follow through in a serve when playing tennis, or when hitting a baseball? Problem 2 A ball at rest has a mass 0.5kg and is kicked with a force of 40N. The impact lasts 0.2s. Find: a) The change in momentum of the ball. b) The final velocity of the ball. Answer: a) 8 Ns, b)16m/s Problem 3 • A football player of mass 130kg travelling at 12.0m/s collides with another player and comes to rest in 0.90s. What was the force of impact? • Answer:1,733N Impulse is the area under the curve in a graph of F vs t. F t Some Engineering Applications Question 6 • Why are airbags used? M A R S E X P L O R A T I O N MARS LANDER AIR BAGS Rover Exits the Lander Applications in Engineering Household Items MILK BOTTLES THE EGG CARTON