Question

(10%) Problem 9: Slick Willy is in traffic court (again) contesting a $50.00 ticket for speeding. The speed limit was vo 50 mph and the police officer clocked Slick going vsw 68 mph. However, he was caught by a police officer driving towards him, so he is arguing that although the police officer measured him to be speeding, in reality he was not. Slick Willy is assuming that the Doppler shift in electromagnetic radiation is described in the same way as the Doppler shift for sound. But note that the speed of electromagnetic radiation in air is about c = 3.0 x 108 m/s, considerably faster than the speed of sound in air. 25% Part (a) If the cop had been stationary, and assuming the radar gun operates at a frequency of g 175 GHz, enter an expression for the frequency,f, of the electromagnetic wave that would have returned to the police car, in terms of the defined quantities. js ( ( v + vo Yv ) c X Incorrect! ▲ 25% Part (b) Now take into account the motion of the police officer toward Slick Willy at a speed of vPO Assume Slick Willy was indeed moving toward the police officer at the speed limit of vo. Enter an expression for the frequency.f, of the electromagnetic wave that would have then returned to the police car, in terms of the defined quantities. 25% Part (c) The police officer confirms that she measured that requency Enter an expression interms o the other det neds eeds for e speed at which the police car must have been moving if Slick Willy were actually driving at the speed limit. To do that, equate the expressions you entered in parts (a) and (b) and solve for vPO. Make use of the low-speedapproximation (1 ± v/OP ~ 1 ± ny c for lyl << c- 25% Part (d) Calculate how fast in miles per hour, the police car must have been moving in order for Slick Willy to have been going at the speed limit

Answer 1

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