As you stand near a railroad track, a train passes by at a speed of 34.5 m/s while sounding its horn at a frequency of 215 hz. what frequency do you hear as the train approaches you and what frequency while it recedes? take the speed of sound in air to be 341 m/s.

when train is approaching then the frequency is 239.2 Hz

when train is moving away  then the frequency is 195.25 Hz    

Explanation:

given,

speed of train = 34.5 m/s

Frequency of sound = 215 Hz

speed of sound = 341 m/s

a) when train is approaching

          f₁ = 239.2 Hz                                

when train is approaching then the frequency is 239.2 Hz

b) when the train is moving away

         f₂ = 195.25 Hz      

when train is moving away  then the frequency is 195.25 Hz                

answer: 802.3 kilo joules of energy represents 191.75 kilo calorie of energy.

explanation:

energy released during combustion of one mole methane = 802.3 kilo joules

if 1 kilo joule = 0.239006   kilo calorie

then ,802.3 kilo joule will be = 802.30.239006 kilo calorie

802.3 kilo joule = 191.75 kilo calorie

hence, the energy in kilo calorie is 191.75 kilo calorie.

when a device is used in a circuit in which the voltage is 81 v, the current flowing through the device is 3 a. what is the resistance of the device?

a. 27 ω

b. 40.5 a

c. 243 ω

d. 243 a

the correct answer is a. 27