Find y ( 5 ) y(5)

Calculus Level pending

Consider the following linear differential equation with constant coefficients

y ( t ) + y ( t ) 6 y ( t ) = 1 , y ( 0 ) = y ( 0 ) = 0 y'' (t) + y'(t) - 6 y(t) = 1, \hspace{12pt} y(0) = y'(0) = 0

Find y ( 5 ) y(5)

Details and Assumptions:

  • y ( t ) = d 2 y d t 2 y''(t) = \dfrac{d^2 y}{d t^2}

  • y ( t ) = d y d t y'(t) = \dfrac{dy}{dt}


The answer is 2202.48.

This section requires Javascript.
You are seeing this because something didn't load right. We suggest you, (a) try refreshing the page, (b) enabling javascript if it is disabled on your browser and, finally, (c) loading the non-javascript version of this page . We're sorry about the hassle.

1 solution

Karan Chatrath
May 13, 2021

y ¨ + y ˙ 6 y = 1 \ddot{y} + \dot{y} - 6y = 1

Taking Laplace transform on both sides:

s 2 Y ( s ) s y ( 0 ) y ˙ ( 0 ) + s Y ( s ) y ( 0 ) 6 Y ( s ) = 1 s s^2Y(s) - sy(0) - \dot{y}(0) + sY(s) - y(0) - 6Y(s) = \frac{1}{s}

y ( 0 ) = y ˙ ( 0 ) = 0 \because y(0) = \dot{y}(0) = 0 ( s 2 + s 6 ) Y ( s ) = 1 s \implies (s^2 + s - 6)Y(s) = \frac{1}{s} Y ( s ) = 1 s ( s 2 + s 6 ) \implies Y(s) = \frac{1}{s(s^2+s-6)} Y ( s ) = 1 s ( s 2 ) ( s + 3 ) \implies Y(s) = \frac{1}{s(s-2)(s+3)} After splitting into partial fractions and simplifying:

Y ( s ) = 1 10 ( s 2 ) 1 6 s + 1 15 ( s + 3 ) Y(s) = \frac{1}{10(s-2)} - \frac{1}{6s} + \frac{1}{15(s+3)}

By performing the inverse Laplace transform on both sides leads to:

y ( t ) = e 2 t 10 1 6 + e 3 t 15 y(t) = \frac{\mathrm{e}^{2t}}{10} - \frac{1}{6} + \frac{\mathrm{e}^{-3t}}{15} y ( 5 ) = e 10 10 1 6 + e 15 15 2202.48 \therefore \boxed{y(5) = \frac{\mathrm{e}^{10}}{10} - \frac{1}{6} + \frac{\mathrm{e}^{-15}}{15} \approx 2202.48}

0 pending reports

×

Problem Loading...

Note Loading...

Set Loading...