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Lecture10

# Of energy nyc the total energy of a system total

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Unformatted text preview: only by amounts of energy that are transferred to or from the system. • The total energy E of an isolated system cannot change isolated system cannot change. NYC – SF by train. On a regular schedule It takes 4 days for 1 way trip One train per day; starts at 1 pm in NYC and arrives in 4 days at 1 pm to SF. Quickly unload – load and go back. (a) Calculate the work of the engine when the train of the mass 10,000 kg accelerates to v = 72 km/h from zero at the departure from NYC. 72 NYC (b) Calculate the work done by the breaks (friction force) when the train slows down from v = 72 km/h to v = 0 arriving to SF. (c) How many other trains will our train meet during one way trip? Lecture 9 Andrei Sirenko, NJIT 29 Lecture 9 Andrei Sirenko, NJIT 30 Potential Energy Curve Sample Problem 8-4 1D Motion • Turning Points • Equilibrium Points A plot of U(x), the potential energy function U( th of a system containing a particle confined to move along the x axis. There is no friction, so mechanical energy is conserved. Lecture 9 Andrei Sirenko, NJIT – Neutral Equilibrium – Unstable Equilibrium Equilibrium – Stable Equilibrium 31 Lecture 9 A 61.0 kg bungee-cord jumper is 61 kg bungee cord jumper is on on a 45.0 m bridge above a river. The elastic bungee cord has a relaxed length of L = 25.0 m. Assume that the cord obeys Hooke’s Hooke’s law, with a spring constant of 160 N/m. If the jumper stops before reaching the jumper stops before reaching the water, water, what is the height h of her feet above the water at her lowest feet above the water at her lowest point? point? Andrei Sirenko, NJIT 32 Sample Problem 7-2 Sample Problem 8-8 Lecture 9 A circus beagle of mass m = 6.0 kg runs onto the left kg runs onto the left end end of a curved ramp with speed v0 = 7.8 m/s at height y0 = 8.5 m above the floor. It then slides to the rig...
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