Pelican Dive: Calculating Escape Height for Fish

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Homework Help Overview

The discussion revolves around a physics problem involving a pelican diving from a height of 20.0 m to catch a fish, focusing on calculating the minimum height at which the fish must spot the pelican to evade capture. The context includes considerations of free fall and time constraints related to the fish's evasive actions.

Discussion Character

  • Exploratory, Mathematical reasoning, Problem interpretation

Approaches and Questions Raised

  • Participants discuss the time it takes for the pelican to reach the water and how to incorporate the fish's evasive time into the calculations. There are attempts to derive equations for motion under gravity and to determine the safe distance for the fish based on these calculations.

Discussion Status

Some participants have provided guidance on the steps to solve the problem, including using kinematic equations. There is an indication that one participant successfully calculated a height based on the suggested approach, but there is no explicit consensus on the method or final answer.

Contextual Notes

Participants mention using approximations for gravitational acceleration and the importance of checking calculations against different values. There is a focus on ensuring the fish has adequate time to evade the pelican.

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Pelicans tuck their wings and free-fall straight down when diving for fish. Suppose a pelican starts its dive from a height of 20.0 m and cannot change its path once committed.If it takes a fish 0.15 s to perform evasive action, at what minimum height must it spot the pelican to escape? Assume the fish is at the surface of the water.
 
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Homeworkboy,
I am a bit rusty with these types of problems, but i believe that i have it.

Where you would start, is to find out how long it would take the pelican to get to the water, regardless of fish.

change in X=20m
acceleration=freefall, or 10m/s2 (its 9.8 to be exact, but im' just using 10)
time=?
starting Velocity=0

so change in X=volt+.5At2

so, you get the time it takes the pelican to reach the water by solving that. Now since the fish can evade in .15 seconds, take the time yu found in the previous problem and subtract .15 from it. This will give you the time that it takes for the pelican to get to .15 seconds away.

Now that you have the time it takes for the pelican to get within evading distance, plug THIS time back into the change in position equation to get the distance from the fish the pelican can be with the fish still being safe.

I would like you to go back through and do the steps, but to check your answer, the answer that i ended up with is 2.8875m.

Good luck in physics!
 
Hey thanks a million! i perfectly understood it...i worked it out the way u said and it came upto 2.86 (since i used 9.8m/s2)...so i checked it and it was the right answer..thanks a lot..
 

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