Solve Force Systems II: Derivatives & Reasoning Explained

In summary, the solution to the problem took the derivative of equation 2 and substituted $F_{1}=57.8$.
  • #1
Drain Brain
144
0
Hello! :)

Here's another problem that I want to fully understand how it was solved.

The part that I'm having a hard time with is the taking-derivatives of some equations. Why did the solver decide to take the derivative of equation 2. And why the second derivative of equation 1 became like that(encircled with red)?
It's the taking-derivatives of things I'm most confused(not the taking derivatives, but the reasoning of the solver why did he take that route.) THANKS!
 

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  • #2
The problem is looking for the minimum \(\displaystyle F_R\), which requires us to take a derivative. (The derivative of a function is 0 at a relative minimum point.) So we set the 1st derivative to 0. Once that is done we need to see if the value of \(\displaystyle F_R\) given by the 1st derivative is a relative minimum or a relative maximum. The 2nd derivative test does this.

As for the second derivative:
The first derivative equation is:
\(\displaystyle 2F_R ~ \frac{d F_R}{d F_1} = 2F_1 - 115.69\)

Taking the derivative with respect to \(\displaystyle F_1\):
\(\displaystyle 2 \frac{d F_R}{d F_1} \cdot \frac{d F_R}{d F_1} + 2 F_R ~ \frac{d^2 F_R}{d F_1 ^2} = 2\)
Now just divide by 2.

(The derivative of the LHS is done by the product rule: \(\displaystyle \frac{d}{dx} f(x)g(x) = \frac{df}{dx} g(x) + f(x) \frac{dg}{dx}\). Also note that I have taken the derivative on the LHS in a different order than your source so it matches the "usual order" when using the product rule.)

-Dan
 
  • #3
Hello Everyone! :)

Just want to ask how did the solution arrive at the part where it substitutes $F_{1}=57.8$(which, I suppose the critical point of the first derivative) and $\frac{d F_R}{d F_1}=0$ to the 2nd derivative.

$\displaystyle \frac{d F_R}{d F_1} \cdot \frac{d F_R}{d F_1} + F_R ~ \frac{d^2 F_R}{d F_1 ^2} = 1$ I only see $\frac{d F_R}{d F_1}$ but not $F_{1}$, where I can substitute their values.

which results in

$\frac{d^2 F_R}{d F_1 ^2}=0.00263>0$ --->>> how did it arrive here? I know what this result means, it tells us the point of minimum. But I don't understand how did that happen.

Need an Immediate help here!
 
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  • #4
Help please! Up! Up! :(
 
  • #5
Drain Brain said:
Help please! Up! Up! :(
Hi Drain Brain:
In the solution notice that equation (2) gives a relation between FR and F1. Once you have F1, simply find FR using equation (2) and replace into the 2nd derivative relation.
 

FAQ: Solve Force Systems II: Derivatives & Reasoning Explained

What are force systems and why are they important in science?

Force systems refer to a collection of forces acting on an object. They are important in science because they help us understand how external forces affect the motion and behavior of objects, and how to predict and control these forces.

How do derivatives play a role in solving force systems?

Derivatives are mathematical tools used to determine the instantaneous rate of change of a function. In force systems, derivatives are used to calculate the change in force over time, which is crucial in understanding the dynamics of the system.

Can derivatives help us reason and make predictions about force systems?

Yes, derivatives allow us to analyze and reason about the behavior of force systems. By using derivatives, we can predict how forces will affect an object's motion, how much force is required to produce a certain movement, and how forces will change over time.

How do we use reasoning to solve force systems?

Reasoning involves using logical thinking and deduction to analyze and understand a problem. In solving force systems, we use reasoning to break down the complex forces acting on an object and determine the most significant factors influencing its motion and behavior.

What are some real-world applications of solving force systems using derivatives and reasoning?

Solving force systems is crucial in many scientific fields, such as physics, engineering, and biomechanics. It has practical applications in designing structures, predicting the movement of objects in space, and understanding the mechanics of the human body, among others.

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