Calculating Cliff Height from Sound Time Delay | Kinematics Question

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SUMMARY

The problem involves calculating the height of a cliff from which a rock is dropped, with the sound of the impact heard 3.2 seconds later. Given the speed of sound at 340 m/s, the total time includes both the fall time of the rock and the time for the sound to travel back up. The correct approach is to separate the time into two components: the time taken for the rock to fall and the time taken for the sound to travel back to the observer. The equations of motion for the rock and sound must be applied to solve for the cliff height.

PREREQUISITES
  • Understanding of kinematic equations, specifically d = vt and d = v1t + 1/2at^2
  • Knowledge of the speed of sound in air (340 m/s)
  • Basic principles of free fall and sound propagation
  • Ability to set up and solve equations with multiple variables
NEXT STEPS
  • Calculate the time taken for the rock to fall using kinematic equations
  • Determine the height of the cliff using the derived equations
  • Explore the relationship between time delay and distance in sound propagation
  • Review examples of similar physics problems involving free fall and sound
USEFUL FOR

Students studying physics, particularly those focusing on kinematics and sound, as well as educators looking for illustrative examples of real-world applications of these concepts.

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Homework Statement


A rock is dropped from a sea cliff, and the sound of it striking the ocean is heard 3.2s later. If the speed of sound is 340 m/s, how high is the cliff.



Homework Equations


d= v1t + 1/2at^2
v2^2 = v1^2 + 2ad



The Attempt at a Solution


I tried using d = vt since we're given the speed of sound and the time taken for the sound to reach our ears. Since sound is unaffected by gravity, i thought i could straightaway use that formula, but I guess I was wrong. This is how far I got up to. Can someone give me a hand?

Thanks
 
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You can use d=vt for the sound. However, note that we are told that 3.2s after the rock is dropped, we hear it hit the ocean, not that the sound takes 3.2s to reach our ears.

Use d=vt to obtain the time taken for the sound to reach out ears iafter the rock hits the ocean(in terms of d). We then know that the rock takes (3.2-t)s to fall. Can you write another equation for the rock as it falls?
 

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