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?

A narrow beam of light from a laser travels through air (n=1.00) and strikes point A on the surface of the water (n=1.33) in a lake. The angle of incidence is $55^{\circ}$. The depth of the lake is 3.0 m. On the flat lake-bottom is point B, directly below point A. (a) If refraction did not occur, how far away from point B would the laser beam strike the lake-bottom? (b) Considering refraction, how far away from point B would the laser beam strike the lake-bottom?

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

A stereo amplifier is rated at $225 \mathrm{~W}$ output at $1000 \mathrm{~Hz}$. The power output drops by $12 \mathrm{~dB}$ at $15 \mathrm{kHz}$. What is the power output in watts at $15 \mathrm{kHz}$ ?

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?

Sunlight is observed to focus at a point 18.5 cm behind a lens. What is its power in diopters?

Two tuning forks oscillate with the same amplitude, but one has twice the frequency. Which (if either) produces the more intense sound?

A dentist's mirror is placed 2.0 cm from a tooth. The enlarged image is located 5.6 cm behind the mirror. (a) What kind of mirror (plane, concave, or convex) is being used? (b) Determine the focal length of the mirror. (c) What is the magnification? (d) How is the image oriented relative to the object?

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)?

Two tuning forks oscillate with the same amplitude, but one has twice the frequency. Which (if either) produces the more intense sound?

A cylindrically shaped piece of collagen (a substance found in the body in connective tissue) is being stretched by a force that increases from $0 \text { to } 3.0 \times 10 ^ { - 2 } \mathrm { N }.$ The length and radius of the collagen are, respectively, 2.5 and 0.091 cm, and Young's modulus is $3.1 \times 10 ^ { 6 } \mathrm { N } / \mathrm { m } ^ { 2 }$

If the stretching obeys Hooke's law, what is the spring constant k for collagen?

The sound level $9.75 \mathrm{~m}$ from a loudspeaker, placed in the open, is $115 \mathrm{~dB}$. What is the acoustic power output (W) of the speaker, assuming it radiates equally in all directions?

A supersonic jet traveling at Mach 2.2 at an altitude of 9500 m passes directly over an observer on the ground. Where will the plane be relative to the observer when the latter hears the sonic boom?

(II) You look directly overhead and see a plane exactly 1.25 km above the ground flying faster than the speed of sound. By the time you hear the sonic boom, the plane has traveled a horizontal distance of 2.0 km. Determine the speed of the plane (the Mach number). Assume the speed of sound is 330 m/s.