15. Two loudspeakers are placed 6.0 m apart. They produce the same sounds, in step, across a frequency range of 1908 Hz to 2471 Hz Point P is located 4.70 m from one loudspeaker and 3.60 m from the other. What frequency of sound from the two speakers will produce constructive interference at point P? Assume the speed of sound is
314 m/s

2420 Hz
2110 Hz
2340 Hz
2190 HZ
2220 Hz

As you are trying to move a heavy box of mass m, you realize that it is too heavy for you to lift by yourself. there is no one around to , so you attach an ideal pulley to the box and a massless rope to the ceiling, which you wrap around the pulley. you pull up on the rope to lift the box. use g for the magnitude of the acceleration due to gravity and neglect friction forces. once you have pulled hard enough to start the box moving upward, what is the magnitude f of the upward force you must apply to the rope to start raising the box with constant velocity? express the magnitude of the force in terms of m, the mass of the box.