Fisherman lifts a trout with his fishing rod directly upwards. The fish is a trout. The trout's mass is 0,45Kg. The trout's acceleration is 2,5m/s^2.
a) draw free body diagram for the trout
b) with how great a force, does the fishing line affect the trout?
The Attempt at a Solution
a) I had great difficulty with drawing the free body diagram of the trout. Especially difficult with regard to action reaction pairs. I didn't really understand what I was supposed to do, but I gave it a try anyway.
b) Newton's laws state that when the net force is positive, then in that case there is acceleration. Also crucially the trout is not at the state of rest. Neither is the trout moving at a constant velocity. This is because the speed is increasing, because the acceleration is constant value of 2,5m/s^2. (these seem to be true according to textbook)
When the net force would be zero, then in those hypothetical cases (not this case), there would be no acceleration. When the acceleration exists then, I suppose the net force must be non-zero amount. ( from the physics textbook)
The questioner stated that the trout did have upwards acceleration = 2,5m/s^2
Therefore it leads to believe that the net force would be upwards. The net force would be some unknown amount, which is positive.
That's as far as I got with my own thinking about it.
I suppose that the weight of the trout= G
.We know that Gtrout = mtrout*atrout
= 0,45kg*9,81m/s^2 = (4,4145kgm)/([s^2]
ca. 4,41 N
In a regular scenario without acceleration, there would exist balance of forces between the trout's weight, and the support force of the fishing line. In such a case, the net force would equal to zero.The trout would stay hanging on the fishing line without acceleration.
But in our scenario there is indeed upwards acceleration. I suppose that the mass of the trout remains the same amount regardless of anything practicalyl. (unless a bigger fish like a shark manages to eat a chunk out of the fish before the fish is reeled in by the fisherman.)
Therefore the force of the line pull upon the trout, would need to increase somehow.
Now that I think about it more. I suppose one could begin from the assumptions of the balanced forces scenario.
Assuming balanced forces inititially. There is now an acceleration of the trout with a= 2,5m/s^2
therefore the pulling force upon the trout has to include:
a= [(2,5m/s^2) + (9,81m/s^2)]
ca. 5,5 N