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Prob Supplement 3 Energy Momentum SOLUTIONS FINAL

# Prob Supplement 3 Energy Momentum SOLUTIONS FINAL -...

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1 Practice Problems Supplement 3 PHY 131 Multiple Choice Questions & Free Response Questions (Work, Energy, Power, Energy & Momentum Conservation; Ch. 7, 8, 9 Giancoli 4 th ed.) SOLUTIONS

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2 Name ________________________________Date ______________ Prof. Pascuzzi PHY 131 Multiple Choice & Short Answer Questions 1) What is the equation for the definition of work? _________________ 2) Is work a vector or a scalar? ____________ Work is a scalar dot product and therefore has no direction . 3) For work to be done on an object, what must be true about the force and displacement? Work can only be done when F and x are either parallel or antiparallel (such as work done by friction), or when a component of a force causing displacement is parallel or antiparallel to the displacement of the object. 4) What does the angle refer to in the work equation? The angle is the angle between the force vector and the displacement vector. 5) What is the definition of power, and how does it relate to work? Power is the rate at which work is done (see equations in 6). “Rate” always means time is in the denominator of a fraction. 6) What are the two equations used for calculating power? Power = ____________________ , Power = ____________________ 7) What are the units of each quantity? a) Work = ______________ b) Power = ____________________ Work units are Joules , or Nm (or kgm 2 /s 2 ) and power units are Watts ( J/s or Nm/s or kgm 2 /s 3 ). 8) Is power a vector or a scalar? _____________________ Power is a scalar quantity, with no direction. 9) What is the equation for an object’s Kinetic Energy? _____ = ______________ 10) What is the equation for an object’s Gravitational Potential Energy? _____ = __________ 11) How is the total mechanical energy of an object written? E tot = _____________________ (if heat Q is involved in the problem, it may be included here. Note that “EPE” is elastic potential energy, which often refers to problems with springs). 12) Based on 9) and 10) above, how do you write the expression for using energy conservation? What does “energy conservation” really mean? “Energy conservation” means that total energy in a problem or situation must be conserved, or constant,
3 both before and after some event (like a collision, explosion or event which involves movement and change of potential energy). You select one location in the problem at which you know v or h , setup the total energy by adding all the energies, then equate that to all of the energy at another point to solve for something in question at the other location. Set up the problem as described in 10) above. 13) Below is a roller coaster along which a 120 kg cart moves with negligible friction. Points A, B, C and D are locations on the track of the roller coaster at which the car passes. The car starts from rest at hilltop A and it has a total energy of 12,000 Joules when it is at point D . B C D Ground A H H D A H B h = 0 a) What is the car’s total energy at B ? ________ = ____________________ (no work needed!) E B = 12,000 Joules b) What is the car’s total energy at A ? ________ = ____________________ (no work needed!) E A = 12,000 Joules c) What is the car’s total energy at C ? ________ = ____________________ (no work needed!) E C = 12,000 Joules d) Using the information above, calculate the car’s speed at point B if the value of H B is 9.0 meters.

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Prob Supplement 3 Energy Momentum SOLUTIONS FINAL -...

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