Apoliceman in a stationary car measures the speed of approaching cars by means of an ultrasonic device that emits a sound with a frequency of 41.2 khz. a car is approaching him at a speed of 33.0 m/s. the wave is reflected by the car and interferes with the emitted sound producing beats. what is the frequency of the beats? the speed of sound in air is 330 m/s.

Four objects each with charge +2.0×10−7c are located at the corners of a square whose sides are 2.0 m long. part a what quantities can be determined using this information? check all that apply. the electric force on a charged object placed at the center of the square. the mass of each object. the total electric potential energy of the system consisting of the four charged objects. part b find the electric force on a charged object placed at the center of the square.