GP #4 Physics 112-1 Fall 2012 Page 1 of 6
Group problem 4: Interference, Sound
and the Doppler effect
At an open-air concert on a hot day (sound speed becomes 347 m/s), a person sits at a location that is
7.00m and 9.10m respectively from speakers at each side of the stage. A musician, warming up, plays a
single 494 Hz tone. Are the speakers in resonance? If so, what resonance? Does constructive or
destructive interference occur?
GP #4 Physics 112-1 Fall 2012 Page 2 of 6
While working in a chemistry lab, you are asked to determine the properties of an unknown gas,
specifically if the gas is monatomic or diatomic. The gas has a density of 1.0 kg/m3 and is kept under
pressure of 8.0 x 104 N/m2. To determine whether the gas is monatomic or diatomic you send sound
wave through the gas and determine that sound travels at a speed of 345 m/s through the gas.
GP #4 Physics 112-1 Fall 2012 Page 3 of 6
You are in charge of calibrating the radar guns for a local police department. One such device emits
microwaves at a frequency of 2.00 GHz. During the trials, these waves are reflected from a car moving
directly away from the stationary emitter. You detect a frequency difference between the received
microwaves and the ones sent out of 293 Hz. Find the speed of the car.
GP #4 Physics 112-1 Fall 2012 Page 4 of 6
Inchy, an inchworm, is inching along your cotton clothesline. The 25m long clothesline has a mass of
1.0kg and is kept taut by a hanging object of mass 10kg. You are hanging up your swimsuit 5.0 m from
one end and you see Inchy 2.5 cm from the opposite end. You pluck the line sending a terrifying 3.0cm
high pulse toward Inchy. If Inchy crawls at 1.0 in/sec, will he get to the end of the clothesline before the
pulse reaches him?
GP #4 Physics 112-1 Fall 2012 Page 5 of 6
Red light emitted by hydrogen atoms at rest in the laboratory has wavelength 656 nm (10-9). Light
emitted in the same process on a distant galaxy is received at Earth with wavelength 708 nm. Describe
the galaxy’s motion relative to Earth.
GP #4 Physics 112-1 Fall 2012 Page 6 of 6
Two piano strings are supposed to be vibrating at 220Hz, but a piano tuner hears three beats every 2.0s
when they are played together. If one is vibrating at 220Hz, what must be the frequency of the other? Is
there only one answer? By what percentage must the tension be increased or decreased to bring them
into tune?