Momentum and Energy Chapter 9, 10, 11 Physics Principles and Problems Zitzewitz, Elliot, Haase,...
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Transcript of Momentum and Energy Chapter 9, 10, 11 Physics Principles and Problems Zitzewitz, Elliot, Haase,...
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Momentum and Energy
Chapter 9, 10, 11Physics Principles and Problems
Zitzewitz, Elliot, Haase, Harper, Herzog, Nelson, Nelson, Schuler and Zorn
McGraw Hill, 2005
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The momentum of an object is the product of that object’s mass and velocity.
p = m • v
Therefore a large oil tanker (big m, small v) and moving bullet (small m, big v) could have equal momentums.
http://www.digicamhistory.com/HaroldEdgertonBulletSmall.jpghttp://kommandobryggan.se/ok/okbilder/oktavius2.jpg
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An impulse changes an object’s momentum. It is the product of force on an object and the
amount of time that force is applied.F • ∆t = m • ∆v
• The same impulse can be delivered in 2 ways: Increasing the force that is applied or increasing
the time the force is applied.
http://discovermagazine.com/2008/the-body/11-turn-your-fist-into-a-blocking-breaking-machine/karate.jpg http://sol.sci.uop.edu/~jfalward/physics17/chapter3/boxingglove.jpg
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Impulse - Momentum TheoremF • ∆t = pf - pi
or F • ∆t = mvf - mvi
• A 2200-kg car traveling at 26-m/s can be stopped in 21-s by applying the brakes or in 0.22-s by hitting a wall. What is the force exerted on the car in both of these situations?
pf = 2200-kg • 0-m/s = 0 pi = 2200-kg • 26-m/s = 57000-kg •m/s
F = pf - pi 0 - 57000 = -2700N OR 0 - 57000 = -260000N ∆t 21 0.22
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Conservation of Momentum
• Within any closed (no change in mass), isolated (external forces are zero) system the momentum is conserved or does not change.
http://webpages.uah.edu/~wilderd/momentum.jpg
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m1v1 + m2v2 = m1v3 + m2v4
where v1 and v2 are the velocities of the objects before the collision and v3 and v4 new velocities after the collision. Notice
the masses haven’t changed.
Elastic Collisions - Objects hit and bounce off
http://img.sparknotes.com/content/testprep/bookimgs/sat2/physics/0002/8ball.gif
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m1v1 + m2v2 = (m1 + m2)v3
where v1 and v2 are the velocities of the objects before the collision and v3 is the new
velocities of the combined masses.
Inelastic Collisions - Objects hit and stick
http://sol.sci.uop.edu/~jfalward/physics17/chapter3/trains.jpg
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Energy, Work and Power
• Energy - the property or ability of an object to produce a change in itself or the world around it.
• Work - a product of the force exerted on an object in the direction of motion and the object’s displacement. W = F • d (unit is the joule = N•m)
• Kinetic Energy - energy resulting from motion. KE = 1/2mv2
• Work-Energy Theorem - work is equal to the change in kinetic energy. W = ∆KE
• Work with Angle - a product of the force and the displacement, times the cosine of the angle between the force and the direction of displacement. W = Fdcos
• Power - work done divided by the time taken to do the work. P = W / t (unit is the watt = J/s)
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Work and Power Problems• The third floor of a house is 8-m above street level. How
much work is needed to move a 150-kg refrigerator to the third floor?
• During a tug-of-war, team A does 2.2 x 105-J of work in pulling team B 8-m. What force did team A exert?
• A wagon is pulled by a force of 38-N exerted on the handle at an angle of 42° with the horizontal. If the wagon is pulled in a circle of radius 25-m, how much work is done?
• A lawn mower is pushed across a lawn by a force of 155-N along the direction of the handle, which is 22.5° above the horizontal. If 64.6-W of power is developed for 90-s, what distance is the mover pushed?