Today is 14 January 2011 -- We had a test on sound waves and to write "Press On" by Calvin Coolidge

Here is the test:

1. Write -- from memory and word-for-word -- the inspirational quotation “Press On” by the 30^th president of the United States, Calvin Coolidge:

"Nothing in the world can take the place of persistence. Talent will not; the world is full of unsuccessful men with talent. Genius will not; unrewarded genius is almost a proverb. Education will not; the world is full of educated derelicts. Persistence and determination alone are omnipotent. The slogan “press on” has solved and always will solve the problems of the human race. "

2. Look at the equation f = v / l.

a. What does each symbol stand for?
f = frequency (times something happens per unit of time)
v = velocity (distance per unit of time, like “meters per second”)
l = wavelength

b. When or how is this equation used?

Find wavelength when frequency and wave velocity are known; find frequency when wavelength and velocity are known; find velocity when wavelength and frequency are known.

c. Compare this equation to the equation relating distance to speed and time at that speed,
S = r x t. (Which term in the distance equation corresponds to which term in the unknown equation?)

S is distance and compares to wavelength

r is rate in units of distance per unit of time and compares to velocity

t is time and relates to frequency which is the number of cycles per unit of time.

3. Answer the following definition questions:
a. What travels at 186,000 miles per second?

Light, electromagnetic radiation in genera

b. How many feet in a mile?

5280 feet per mile

c. How many centimeters in one inch?

2.54 cm per inch

4. A tube closed at one end is 13 cm long. Blowing across the open end of the tube makes a standing sound wave.
a. How much of the wave is in the tube?

¼ of wave is in closed-end tube.

b. What is the length of the full wave?

Since ¼ fits in tube, full wave must be 4 x 13cm = 52 cm.

c. The frequency of the wave is 644.77 per second. Calculate the speed of sound for this condition.
v = f x l = 644.77/sec x 52 cm = 33,528 cm / sec

d. The period of a wave is the reciprocal of its frequency, P = 1/f. What is the period of the wave?

P = 1 / 644.77 / sec = 0.00155 seconds
5. Are sound waves longitudinal or transverse? How can you show this?
Longitudinal. They are compressive which gives rise to the Doppler effect.

6. “The cheetah is capable of speed up to 72 mph (114 km/h) and can maintain this speed over an average prey chase of 3.5 miles."
a. How long will the cheetah run at this speed?
Use equation for distance: S = r x t. Rearrange to solve for time: S / r = t = 3.5 mile/72 mile/hr.

= 0.0486 hr. For minutes, multiply by 60 min/hr for 2.91 minutes.

b. If a marathon runner can go 15 mph (for 26 miles), what minimum distance ahead of the cheetah does he have to be to keep from being the cheetah’s lunch? Assume that the cheetah stops running exactly at 3.5 miles. (This problem is a little tricky but you can do it if you THINK!)

The runner has to be far enough ahead so that the cheetah can’t catch him in 2.91 minutes. In that time, the runner can go S = r x t = 15 m / hr x 0.0486 hr = 0.729 mile. That means he has to be 3.5 – 0.729 miles or 2.771 miles.

c. You will be relieved to know that the marathoner escaped the cheetah! If his home village is the same distance as his minimum distance, and he shouts very loud “I’m safe!” how long will the sound of his voice take to reach the village?

Since sound travels 1100 ft / sec, and there are 5280 feet per mile, the time it takes the sound to reach the village is (2.771 miles x 5280 feet / mile) / 1100 ft/sec = 13.3 seconds.