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allsm [11]
3 years ago
12

A train is traveling away from you at 120 km/h. it blows its whistle, and you hear a tone of 0.400 kHz. Take the speed of sound

to be 340 m/s. What frequency does the whistle actually produce? A) 444 Hz. B) 439 Hz C) 364 Hz D) 361 Hz
Physics
1 answer:
Vaselesa [24]3 years ago
5 0

Answer:B)439.21 Hz

Explanation:

Given

velocity of train v=120 km/h\approx 120\times \frac{5}{18}=33.33 m/s

frequency of train f_a=0.400 kHz\approx 400 Hz

speed of sound c=340 m/s

frequency from Doppler effect can be calculated by

f_a=(\frac{c}{c+v})\cdot f

400=(\frac{340}{340+33.33})\cdot f

400=\frac{340}{373.33}\cdot f

f=400\times 1.098

f=439.21 Hz

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vovikov84 [41]

Complete Question

In an action movie, the villain is rescued from the ocean by grabbing onto the ladder hanging from a helicopter. He is so intent on gripping the ladder that he lets go of his briefcase of counterfeit money when he is 130 m above the water. If the briefcase hits the water 6.0 s later, what was the speed at which the helicopter was ascending?

Answer:

The speed of the helicopter is u  =  7.73 \  m/s

Explanation:

From the question we are told that

   The height at which he let go of the brief case is  h =  130 m  

    The  time taken before the the brief case hits the water is  t =  6 s

Generally the initial speed of the  briefcase (Which also the speed of the helicopter )before the man let go of it is  mathematically evaluated using kinematic equation as

      s = h+  u t +  0.5 gt^2

Here s  is the distance covered by the bag at sea level which is zero

      0 = 130+  u * (6) +  0.5  *  (-9.8) * (6)^2

=>    0 = 130+  u * (6) +  0.5  *  (-9.8) * (6)^2

=>   u  =  \frac{-130 +  (0.5 * 9.8 *  6^2) }{6}

=>   u  =  7.73 \  m/s

     

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A rock, initially at rest with respect to Earth and located an infinite distance away is released and accelerates toward Earth.
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in an isolated system, two cars, each with a mass of 1,500 kg, collide. car 1 is initially at rest while car 2 is moving at 5 m/
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Explanation:

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