College Physics time and distance question

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you are standing on the rim of a canyon. You drop a rock and in 7.0s hear the sound of it hitting the bottom (the speed of sound in air is about 340m/s)

Calculate how fast the rock is traveling when it hits the bottom?

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Explanation & Answer

You can hear the sound of rock  after  7 seconds of getting dropped

Here we have to consider the time the rock takes to hit the ground before it makes a sound by hitting

The total time = time taken by rock to hit the ground +time for the sound to return up the canyon

Total time = a+b

a.Time taken for rock to fall/hit the ground 

    d=1/2gt^2 {g=9.8}

     t=square root of (2d/g)

b.Time for the sound to return up the canyon

speed of sound in air is 340m/s

t=d/340(as Distance = Velocity* Time )

Total time =7

So we have 

Square root of (2d/9.8) +d/340=7{calculate this and you get the answer)

Solve d 

Distance of canyon is 

------ sec for the rock to drop  

------- sec for the return sound

Let me tell you the other experts answerwhich you bested  is incorrect even the multiplication is wrong just multiply 340*7 =2380

This is great! Exactly what I wanted.