Why does this display work better on a noisy day than on a quiet day?

A fireworks shell explodes $100 \mathrm{~m}$ above the ground, creating colorful sparks. How much greater is the sound level of the explosion for a person at a point directly below the explosion than for a person a horizontal distance of $200 \mathrm{~m}$ away?

The diameter $D$ of a tube does affect the node at the open end of a tube. The end correction can be roughly approximated as adding $D / 3$ to $\ell$ to give us an effective length for the tube in calculations. For a closed tube of length $0.55 \mathrm{~m}$ and diameter $3.0 \mathrm{~cm}$, what are the frequencies of the first four harmonics, taking the end correction into consideration?

The diameter $D$ of a tube does affect the position of the antinode at the open end of a tube. The end correction can be roughly approximated by adding $D / 3$ to $\ell$ to give us an effective length for the tube in calculations. For a closed tube of length $55.0 \mathrm{~cm}$ and diameter $3.0 \mathrm{~cm}$, what are the first four harmonics, taking the end correction into consideration?

Carbon dioxide enters an adiabatic compressor at 100 kPa, 300 K and exits at 1000 kPa, 520 K. Find the compressor efficiency and the entropy generation for the process.

Carbon dioxide enters an adiabatic compressor at 100 kPa and 300 K at a rate of 1.8 kg/s and exits at 600 kPa and 450 K. Neglecting the kinetic energy changes, determine the isentropic efficiency of the compressor.

A particular whistle produces sound by setting up the fundamental standing wave in an air column $7.10 \mathrm{~cm}$ long. The tube is closed at one end. The whistle blower is riding in a car moving away from you at $25 \mathrm{~m} / \mathrm{s}$. What frequency do you hear?

The frequency of a steam train whistle as it approaches you is $552 \mathrm{~Hz}$. After it passes you, its frequency is measured as $486 \mathrm{~Hz}$. How fast was the train moving (assume constant velocity)?

A person struggles to read by holding a book at arm's length, a distance of 45 cm away (= near point). What power of reading glasses should be prescribed for him, assuming they will be placed 2.0 cm from the eye and he wants to read at the normal near point of 25 cm?

A science museum has a display called a sewer pipe symphony. It consists of many plastic pipes of various lengths, which are open on both ends. (a) If the pipes have lengths of $3.0 \mathrm{~m}, 2.5 \mathrm{~m}$, $2.0 \mathrm{~m}, 1.5 \mathrm{~m}$ and $1.0 \mathrm{~m}$, what frequencies will be heard by a visitor's ear placed near the ends of the pipes?

For the problem, identify all the forces acting on the object and draw a free-body diagram of the object. A box is being dragged across the floor at a constant speed by a rope pulling horizontally on it. Friction is not negligible.

A certain dog whistle operates at 23.5 kHz, while another (brand X) operates at an unknown frequency. If neither whistle can be heard by humans when played separately, but a shrill whine of frequency 5000 Hz occurs when they are played simultaneously, estimate the operating frequency of brand X.

Explain how hyposensitization is achieved and suggest credible mechanisms by which it might work.

A fish finder uses a sonar device that sends $20,000-\mathrm{Hz}$ sound pulses downward from the bottom of the boat, and then detects echoes. If the maximum depth for which it is designed to work is $75 \mathrm{~m}$, what is the minimum time between pulses (in fresh water)?