A super giant star Betelgeuse has a surface temperature of about 2900 K and powe

Question

A super giant star Betelgeuse has a surface temperature of about 2900 K and power (in joules per second or watts) of approximately 4 times 10^30 W. Assume that Betelgeuse is a perfect emitter (emissivity e = 1) and spherical, find it radius. If a product of a pressure and volume (pV) of an ideal gas remains constant. A) the pressure remains constant, B) energy is added as heat, C) work is done on the gas, D) the temperature is constant, F) no energy enters or leaves as heat In doing 16 600 J of work, an engine rejected 9700 J of heat. What is the efficiency of the engine? The linear density of the A string on a violin is 7.8 times 10^-4 kg/m. A wave on the string has a frequency of 440 Hz and a wavelength of 65 cm. What is the tension in the string? Transverse waves travel on each string of an electric guitar after the string is plucked (see Figure 16.8). The length of each string between its two fixed ends is 0.628 m, and the mass is 0.208 g for the highest pitched E string and 3.32 g for the lowest pitched E string. Each string is under a tension of 226 N. Find the speeds of the waves on the two strings. AM and FM radio waves are transverse waves consisting of electric and magnetic disturbances traveling at a speed of 3.00 times 10^9 m/s. A station broadcasts an AM radio wave whose frequency is 1230 times 10^8 Hz (1230 kHz on the dial) and an FM radio wave whose frequency is 91.9 times 10^6 Hz (91.9 MHz on the dial). Find the distance between adjacent crests in each wave.

Explanation / Answer

15) Q = e*sigma*T^4A*t

A = 4pir^2

r = sqrt((Q/t)/4pi*e*sigma*T^4)

r = sqrt(4*10^30/4*3.14*5.6*10^-8*2900^4)

r = 3*10^11 m

16) the product of p and v is the work done on the gas

17) efficiency = w/Q in

Q in = 16600+9700 = 25700 J

efficiency = 16600/25700 = 0.622

that is 62.2 %

18) v = sqrt(T/m)

here m is the linear density

v = lambda*f = 286 m/s

T = 286^2*7.8*10^-4 = 63.8 N

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