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MT1Review

MT1Review - Practice Problems for 7C Exam 1 Problem 1 A...

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Practice Problems for 7C Exam 1 September 27, 2009 Problem 1 A thin cylindrical object of mass m and cross-sectional area A is being levitated by shining a laser that emits light incident normal to the bottom face of the object. Assume it is reflective and the cross-section of the laser beam is the same as the object. a. What is the power P (energy emitted per unit time) necessary to keep the object levitated? For a typical laser emitting 1 W of power, what mass does this correspond to? b. In terms of P , A , and physical constants, what is the amplitude of the magnetic field B o , coming from the laser? c. In some coordinate system, the magnetic field incident on the object can be written B = B o sin( kx - wt y . Write the corresponding electric field in terms of the preceding quantities. d. Could we have written B = B o cos( kx - wt x ? Explain. e. Could we have written B = B o sin( kx 2 - wt y ? Explain. Problem 2 A rocket ship traveling in the positive x direction relative to Earth ob- servers. It has speed of 4 5 c . Billy is standing at the rear of the ship and Mary

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