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3 years ago

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Lifting a stone block 146m to the top of the Great Pyramid required 146,000 J of work. How much work was done to lift the block

halfway to the top?
A. 36,500 Joules
B. 73,000 Joules
C. 146,000 Joules
D. 292,000 Joules
Please help me.

1 answer:

ASHA 777 [7]3 years ago

3 0

B is your answer to the question

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Answer:

a) f' = 432 Hz

b) I = 8.12*10^-4 W/m^2

Explanation:

a) To calculate the frequency of sound waves that car receives, you take into account the Doppler effect. In this case (observer moves away of the source) you have the following formula:

$f'=f(\frac{v-v_o}{v+v_s})$ (1)

where

f: frequency of the source = ?

v: speed of sound = 343 m/s

vo: speed of the observer = 40.0 m/s

vs: speed of the source = 0 m/s (stationary)

You replace the values of all parameters in the equation (1):

To calculate f' you first calculate the frequency of the sound wave, by using the following formula:

$v=\lambda f\\\\$

v: speed of sound

λ: wavelength = 0.700 m

$f=\frac{v}{\lambda}=\frac{343m/s}{0.700m}=480Hz$

Next, you replace the values of all parameters in the equation (1):

$f'=(490Hz)(\frac{343m/s-40.0m/s}{343m/s})=432Hz$

hence, the frequency perceived by the car is 432 Hz

b) To calculate the power of the sound wave, when the car is 70.0 maway from the speaker, you use the following formula:

$I=\frac{P}{4\pi r^2}$

P: power of the source = 50.0 W

r: distance to the source = 70.0 m

$I=\frac{50.0 W}{4\pi(70.0m)^2}=8.12*10^{-4}\frac{W}{m^2}$

hence, the intensity is 8.12*10^⁻4 W/m^2

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3 years ago