# Need help with salmon problem

1. Sep 24, 2006

### Touchme

salmon motion problem

Hi,

A Chinook Salmon has a maximum underwater speed of 3.58 m/s, but it can jump out of water with a speed of 6.68 m/s. to move upstream past a waterfall, the salmon does not need to jump to the top of the fall, but only to a point in the fall where the water speed is less than 3.58 m/s; it can then swim up the fall for the remaining distance. Because the salmon must make forward progress in the water, let's assume that it can swim to the top if the water speed is 3.00 m/s. If water has a speed of 1.40 m/s as it passes over a ledge, how far below the ledge will the water be moving with a speed of 3.00 m/s? (Note that water undergoes projectile motion once it leaves the ledge.)

If the salmon is able to jump vertically upward from the base of the fall, what is the maximum height of waterfall that the salmon can clear?

I tried using 6.68 as initial velocity, determine the time when it reaches max height (final velocity = 0). I use the time, initial velocity, and 9.8 to solve for the max height. The answer i got was 2.2766 m and its wrong. Can someone help me with this problem. Thank you

Last edited: Sep 24, 2006
2. Sep 24, 2006

### andrevdh

The waterfall is parabolic motion of "pieces" of water. I assume that a piece of water leaves the ledge horizontally with a speed of 1.40 m/s. As this piece of water travels along a parbolic path its speed increases. You need to calculate the vertical distance below the ledge where such a piece of water reaches a speed of 3.00 m/s. The salmon need to be able to jump up to this point in order to swim the remaining distance up to the ledge. Note that the answer asks the height of the ledge above the point where the salmon leaves the stream while jumping up to this point in the waterfall. So the answer is the sum of these two distances - jumping height and distance below ledge.

3. Sep 24, 2006

### Touchme

Thank you for clarifying what the question is asking for and thanks for the tip.

4. Sep 24, 2006

### andrevdh

Remember that the speed of a projectile is determined by its both its velocity components.

5. Sep 27, 2006

### parwana

so how do u do part b- If the salmon is able to jump vertically upward from the base of the fall, what is the maximum height of waterfall that the salmon can clear?? I cant get it right

6. Sep 28, 2006

### andrevdh

What have you been able to determine thus far?

The maximum jumping height? What do you get for this distance?

The distance below the ledge where the water reaches a speed of 3.00 m/s?

7. Sep 28, 2006

### parwana

I got the distance below the ledge= .3 m

8. Sep 28, 2006