How Does the Archerfish Use Projectile Motion to Hunt?

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SUMMARY

The archerfish utilizes projectile motion to hunt by expelling water at an initial speed of 2.36 m/sec at an angle of 20.7 degrees. The vertical component of this velocity is calculated using the sine function, yielding 0.83 m/sec. To determine how long the beetle has to react, one must analyze the vertical component of the water stream's velocity when it reaches the beetle. The discussion emphasizes the need to treat horizontal and vertical motions separately to solve for the height of the beetle and the horizontal distance from the fish.

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The archerfish hunts by dislodging an unsuspecting insect from its resting place with a stream of water expelled from the fish's mouth. Suppose the archerfish squirts water with an initial speed of 2.36 m/sec at an angle of 20.7 degrees above the horizontal. When the stream reachs the beetle a height h avoe the water's surface it is moving horizontal.

https://wug-s.physics.uiuc.edu/cgi/courses/shell/common/showme.pl?cc/DuPage/Phys1201/fall-evening/homework/Ch-04-2D-Motion/wt-archer-fish/archer-fish.gif

(a) What is the vertical component of the water's initial velocity?

I got 0.83 for part a. I did 2.36cos(20.7)

(b) How long does the bettle have to react?

I don't know what to do for this one.

(c) How high is the bettle above the fish?

Would you use d= (vi +vf)/2 x t. You would use the time found in part b right?

(d) What is the horizontal distance between the fish and the bettle?

I'm confused about this one too.
 
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Very nice picture, indeed!

wolves5 said:
(a) What is the vertical component of the water's initial velocity?

I got 0.83 for part a. I did 2.36cos(20.7)
You calculated with sine instead of cosine, I am afraid.

wolves5 said:
(b) How long does the bettle have to react?

I don't know what to do for this one.

Read the problem, the water stream is horizontal when it reaches the beetle. What is the vertical component of velocity there?
How do you get the vertical component of velocity in terms of time?

wolves5 said:
(c) How high is the bettle above the fish?

Would you use d= (vi +vf)/2 x t. You would use the time found in part b right?

What are vi and vf? Take care, this is a two-dimensional motion, you need to treat the horizontal and vertical components separated. And yes, you can use the time you got in part b.

wolves5 said:
(d) What is the horizontal distance between the fish and the bettle?

I'm confused about this one too.

This is projectile motion and it can be decomposed into a vertical motion and a horizontal one. What is the velocity of the horizontal motion?

ehild
 

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