Harbor seals, like many animals, determine the direction from 30 which a sound is coming by sensing the difference in arrival times at their two ears. A small difference in arrival times means that the object is in front of the seal; a larger difference means it is to the left or right. There is a minimum time difference that a seal can sense, and this leads to a limitation on a seal's direction sense. Seals can distinguish between two sounds that come from directions $3^{\circ}$ apart in air, but this increases to $9^{\circ}$ in water. Explain why you would expect a seal's directional discrimination to be worse in water than in air.

Explain why helium-filled balloons deflate over time faster than air-filled balloons do.

A laser beam has intensity $I _ { 0 }$. a. What is the tensity, in terms of $I _ { 0 }$, if a lens focuses the laser beam to 1/10 its initial diameter? b. What is the intensity, in terms of $I _ { 0 }$, if a lens defocuses the laser beam to 10 times its initial diameter?

A wave pulse travels along at string at a speed of 200 cm/s. What will be the speed if: a. The string's tension is doubled? b. The string's mass is quadrupled (but its length is unchanged)? c. The string's length is quadrupled (but its mass is unchanged)? d. The string's mass and length are both quadrupled? Note that parts a - d are independent and refer to changes made to the original string.

A common trick for opening a stubborn lid on a jar is to run very hot water over the lid for a short time. Explain how this helps to loosen the lid.

a. In your own words, define what a longitudinal wave is. b. Give an example of a wave that, from your own experience, you know is a longitudinal wave. What observations or evidence tells you this is a longitudinal wave?

An oscillator creates periodic waves on a stretched string.

a. IF the period of the oscillator doubles, what happens to the wavelength and wave speed? The wavelength doubles but the wave speed is unchanged. The wavelength is halved but the wave speed is unchanged. The wavelength is unchanged but the wave speed doubles.

b. If the amplitude of the oscillator doubles, what happens to the wavelength and wave speed? Both wavelength and wave speed are unchanged. The wavelength is unchanged but the wave speed doubles. The wavelength doubles but the wave speed is unchanged.

When in the air, a waterproof speaker emits sound waves that have a frequency of $1000 \mathrm{~Hz}$. When the speaker is lowered into the water, does the frequency of the sound increase, decrease, or remain the same? Does the wavelength of the sound increase, decrease, or remain the same?

a. In your own words, define what a transverse wave is. b. Give an example of a wave that, from your own experience, you know is a transverse wave. What observations or evidence tells you this is a transverse wave?

A ball of mass m oscillates on a spring with spring constant k = 200 N/m. The ball's position is x = (0.350 m) cost (15.0 t), with t measured in seconds. a. What is the amplitude of the ball's motion? A. 0.175 m B. 0.350 m C. 0.700 m D. 7.50 m E. 15.0 m b. What is the frequency of the ball's motion? A. 0.35 Hz B. 2.39 Hz C. 5.44 Hz D. 6.28 Hz E. 15.0 Hz c. What is the value of the mass m? A. 0.45 kg B. 0.89 kg C. 1.54 kg D. 3.76 kg E. 6.33 kg d. What is the total mechanical energy of the oscillator? A. 1.65 J B. 3.28 J C. 6.73 J D. 10.1 J E. 12.2 J e. What is the ball's maximum speed? A. 0.35 m/s B. 1.76 m/s C. 2.60 m/s D. 3.88 m/s E. 5.25 m/s

To determine an athlete's body fat, she is weighed first in air and then again while she's completely underwater. It is found that she weighs 690 N when weighed in air and 42 N when weighed underwater. What is her average density?

You are listening to music from a loudspeaker. Then a second speaker is turned on. Is it possible that the music you now hear is quieter than it was with only the first speaker playing? Explain.

Th lowest pressure ever obtained in a laboratory setting is $4.0 \times 10 ^ { - 11 } \mathrm { Pa }$. At this pressure, how many molecules of air would there be in a $20 ^ { \circ } \mathrm { C }$ experimental chamber with a volume of $0.090 \mathrm { m } ^ { 3 }$?

A box is 200 cm wide, 40 cm deep, and 3.0 cm high. What is its volume in $m ^ { 3 }$?