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44: A wave travels along a string at a speed of 280~m/s. What will be the speed if the string is replaced by one made of the same material and under the same tension but having twice the radius?
54: A wave on a string is described by
D(x,t) = (2.00 cm)*sin[(12.57 rad/m)*x - (638 rad/s)*t],
where x is in m and t is in s. The linear density of the string is 5.00 g/m. What are66: Lasers can be used to drill or cut material.
One such laser generates a series of high-intensity pulses
rather than a continuous beam of light.
Each pulse contains 500 mJ or energy and lasts 10 ns.
The laser fires 10 such pulses per second.
(a) What is the peak power of the laser light?
The peak power is the power during one of the 10 ns pulses.
(b) What is the average power output of the laser?
The average power is the total energy delivered per second.
(c) A lens focuses the laser beam to a
10-µm-diameter circle on the target.
During the pulse, what is the light intensity on the target?
(d) The intensity of sunlight at midday is
about 1100 W/m2.
What is the ratio of the laser intensity on the target
to the intensity of the midday sun?
72: A physics professor demonstrates the Doppler effect by tying a 600 Hz sound generator to a 1.0-m-long rope and whirling it around her head in a horizontal circle at 100 rpm. What are the highest and lowest frequencies heard by a student in the classroom?
76: Wavelengths of light from a distant galaxy are found to be 0.5% longer than the corresponding wavelengths measured in a terrestrial laboratory. Is the galaxy approaching or receding from the earth? At what speed?