Equilibrium of Force System

The body is said to be in equilibrium if the resultant of all forces acting on it is zero. There are two major types of static equilibrium, namely, translational equilibrium and rotational equilibrium.
 

Formulas
Concurrent force system
$\Sigma F_x = 0$

$\Sigma F_y = 0$
 

Parallel Force System
$\Sigma F = 0$

$\Sigma M_O = 0$
 

Non-Concurrent Non-Parallel Force System
$\Sigma F_x = 0$

$\Sigma F_y = 0$

$\Sigma M_O = 0$
 

Problem 03 | Laplace Transform by Integration

Problem 03
Find the Laplace transform of   $f(t) = \sin bt$.
 

Problem 03
$\displaystyle \mathcal{L} \left\{f(t)\right\} = \int_0^\infty e^{-st} f(t) \, dt$

$\displaystyle \mathcal{L} (\sin bt) = \int_0^\infty e^{-st} \sin bt \, dt$
 

For   $\displaystyle \int_0^\infty e^{-st} \sin bt \, dt$.

Using integration by parts:   $\displaystyle \int u\,dv = uv - \int v\, du$.   Let

Problem 02 | Laplace Transform by Integration

Problem 02
Find the Laplace transform of   $f(t) = e^{at}$.
 

Solution 02
$\displaystyle \mathcal{L} \left\{f(t)\right\} = \int_0^\infty e^{-st} f(t) \, dt$

$\displaystyle \mathcal{L} (e^{at}) = \int_0^\infty e^{-st} e^{at} \, dt$

$\displaystyle \mathcal{L} (e^{at}) = \int_0^\infty e^{-st + at} \, dt$

$\displaystyle \mathcal{L} (e^{at}) = \int_0^\infty e^{-(s - a)t} \, dt$

$\displaystyle \mathcal{L} (e^{at}) = -\dfrac{1}{s - a} \int_0^\infty e^{-(s - a)t} \, [ \, -(s - a) \, dt \, ]$

Problem 01 | Laplace Transform by Integration

Problem 01
Find the Laplace transform of   $f(t) = 1$   when   $t > 0$.
 

Solution 01
$\displaystyle \mathcal{L} \left\{f(t)\right\} = \int_0^\infty e^{-st} f(t) \, dt$

$\displaystyle \mathcal{L} (1) = \int_0^\infty e^{-st} (1) \, dt$

$\displaystyle \mathcal{L} (1) = \int_0^\infty e^{-st} \, dt$

$\displaystyle \mathcal{L} (1) = -\dfrac{1}{s} \int_0^\infty e^{-st} \, (-s \, dt)$

$\displaystyle \mathcal{L} (1) = -\dfrac{1}{s} \left[ e^{-st} \right]_0^\infty$

Laplace Transform

Definition of Laplace Transform

Let   $f(t)$   be a given function which is defined for   $t \ge 0$. If there exists a function   $F(s)$  so that
 

$\displaystyle F(s) = \int_0^\infty e^{-st} \, f(t) \, dt$,

 

then   $F(s)$   is called the Laplace Transform of   $f(t)$, and will be denoted by   $\mathcal{L} \left\{f(t)\right\}$.   Notice the integrator   $e^{-st} \, dt$   where   $s$   is a parameter which may be real or complex.
 

Engineering Economy

Simple Interest, Compounded Interest, Annuity, Capitalized Cost, Annual Cost, Depreciation, Depletion, Capital Recovery, Property Valuation or Appraisal, Principles of Accounting, Cost Accounting, Break-even Analysis, Minimum Cost Analysis, Public Economy, Inflation and Deflation, Risk and Uncertainty.

Topics so far...