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CHAPTER 9 NOTES KONICHEK • I. Impulse and change in momentum • A. Newton wrote his 3 laws in terms of momentum- quantity of motion • B. Momentum is the product of the mass and the velocity of an object. • 1. symbol is p, so p=mv vector quantity • a. units: Kgm/s • C. If a single body has no net forces acting on it, its momentum is conserved. • D. Impulse theorem- Ft=p Newton’s 2nd law can be derived from this • 1. (F)Δt= M(V2 – V1) • 2. Often the force isn’t constant during exertion. Therefore average force is used in the equation • 3. A large change in momentum occurs when there is a large impulse force • a. a large impulse can result can result from a large force acting over a short time • 1. a car crash-The air bags increase the contact time against the dash, so the impulse force isn’t as great. • SAMPLE PROBLEM- A BASEBALL OF MASS .14Kg moving at 35m/s • a. find the momentum of the baseball • p=mv- p= (.14Kg)35m/s=4.9Kgm/s • b. find the velocity at which a bowling ball mass of 7.26Kg would have to equal the momentum of the baseball • 4.9Kgm/s=7.26KgVbb =.67m/s • • ANOTHER PROBLEM • An engine of the orbital maneuvering system (OMS) on a space shuttle exerts a force of 30000 N j for 4.00 s, exhausting a negligible mass of fuel relative to the 95,000 kg mass of the shuttle. (a) What is the impulse of the force for this 4.00 s? • (b) What is the shuttle's change in momentum from this impulse? (c) What is the shuttle's change in velocity from this impulse? (d) Why can't we find the resulting change in kinetic energy of the shuttle? • • Answer to Example Impulse Problems • • a. Impulse = Ft = 30000(4) = 120000 N-s b. change in momentum = impulse(FΔt) = 120000 N-s c. FΔt = m∆v 120000 = (95000)∆v ∆v = 1.26 m/s d. We do not know the initial velocity. • SAMPLE PROBLEM- IMPULSE AND MOMENTUM • A .02Kg golf ball strikes a guy in the head with a velocity of 90m/s. The ball strikes and bounce off in .06s. Find the impulse forces off their head. • FΔt= MΔV F= M( V2-V1)/Δt • F= .2Kg(0-90m/s)/.06s= -300N • 1. like getting hit with a 13 pound club in the head • II. ANGULAR MOMENTUM • A. the quantity of angular motion that is similar to linear momentum • 1. No torque. The angular momentum is constant • 2. angular momentum is the product of the mass , velocity, and the distance from the center of rotaion, and the distance perpendicular to that distance. • a. IiI= Iff I= angular momentum, is angular velocity