Theresa Hoffmann, LCPC Alan Mandell, PhD Copyright: 2011 T. Hoffmann.
Wednesday 6/3 PHYS 2010 Nathalie Hoffmann University of Utah.
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Transcript of Wednesday 6/3 PHYS 2010 Nathalie Hoffmann University of Utah.
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Wednesday 6/3PHYS 2010
Nathalie HoffmannUniversity of Utah
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Spring Force
• Hooke’s Law
• k is the spring constant• x > 0 for extension, x < 0 for compression
• Spring force is a restoring force• It acts in the opposite direction of displacement, trying to restore the spring
to its equilibrium position
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Spring Potential Energy
• k is the spring constant• X is the displacement from the spring’s equilibrium position
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Momentum
• Momentum is a vector, (has components!)
• Conservation of momentum?
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Conservation of momentum
• Total momentum of the system is conserved in collisions
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Collisions
• Elastic collision• Momentum is conserved• Kinetic energy is conserved
• Inelastic collisions• Only momentum is conserved
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Notes
• Proton & neutron have essentially the same mass: 1.67 x 10-27
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Practice Problems
• A spring that has a spring constant of 200 N/m is oriented vertically with one end on the ground. (a) What distance does the spring compress when a 2.00-kg object is placed on its upper end? (b) By how much does the potential energy of the spring increase during the compression?
• You may have noticed runaway truck lanes while driving in the mountains. These gravel-filled lanes are designed to stop trucks that have lost their brakes on mountain grades. Typically such a lane is horizontal (if possible) and about 35.0 m long. We can think of the ground as exerting a frictional drag force on the truck. If the truck enters the gravel lane with a speed of 55.0 mph (24.6 m/s), use the work-energy theorem to find the minimum coefficient of kinetic friction between the truck and the lane to be able to stop the truck.
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Practice Problems
• In 2006, NASA’s Mars Odyssey orbiter detected violent gas eruptions on Mars, where the acceleration due to gravity is 3.7 m/s2. The jets throw sand and dust about 75.0 m above the surface. (a) What is the speed of the material just as it leaves the surface? (b) Scientists estimate that the jets originate as high-pressure gas speeds through vents just underground at about 160 km/h. How much energy per kilogram of material is lost due to nonconservative forces as the high-speed matter forces its way to the surface and into the air?
• A spring that is compressed 12.5 cm from its equilibrium position stores 3.33 J of potential energy. Determine the spring constant.
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Answers
• P1.1: x = 9.80 cm, U = 0.960 J• P1.2: μ = 0.882• P1.3: • P2.1: v = 24 m/s, E = 710 J/kg lost to non-conservative forces• P2.2: k = 426 N/m• P2.3: