PHYS171_f11_exam_4_practice_solution - PHYS171 Exam 4...

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PHYS171 Exam 4 practice Fall 2011 Name: _____________________ Student ID #: ________ 1 Questions/Problems 1) Explain why it is not practically possible for a particle to be accelerated to a speed greater than the speed of light. (The relativistic equations given at the end of this exam may be of use.) (5 points) We may use the expression for the momentum, mv p γ = . As the velocity approaches the speed of light the factor () 2 1 2 2 1 c v = approaches infinity. A force is necessary to change momentum, and infinite force would be necessary to acceleration to particle beyond the speed of light. ( F = dp / dt ). One could also argue based on the expression for energy, 2 mc E = . Again, infinite energy is needed to achieve the speed of light. 2) Explain why an object less dense than water will rise to the surface if immersed in a tank of water. Be quantitative (10 points) The object will move if there is a net force. If the object is of finite size, the pressure on the bottom surface will be higher than the pressure on the top surface, since
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This note was uploaded on 12/29/2011 for the course PHYSICS 171 taught by Professor La porta during the Fall '11 term at Maryland.

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PHYS171_f11_exam_4_practice_solution - PHYS171 Exam 4...

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