A mass weighing 4 lb stretches a spring 2 in. Suppose that the mass is given an additional 6-in displacement in the positive direction and then released. The mass is in a medium that exerts a viscous resistance of 6 lb when the mass has a velocity of 3 ft/s. Under the assumptions discussed in this section, formulate the initial value problem that governs the motion of the mass.

Respuesta :

Answer:

[tex]\frac{1}{8} y'' + 2y' + 24y=0[/tex]

Explanation:

The standard form of the 2nd order differential equation governing the motion of mass-spring system is given by

[tex]my'' + \zeta y' + ky=0[/tex]

Where m is the mass, ζ is the damping constant, and k is the spring constant.

The spring constant k can be found by

[tex]w - kL=0[/tex]

[tex]mg - kL=0[/tex]

[tex]4 - k\frac{1}{6}=0[/tex]

[tex]k = 4\times 6 =24[/tex]

The damping constant can be found by

[tex]F = -\zeta y'[/tex]

[tex]6 = 3\zeta[/tex]

[tex]\zeta = \frac{6}{3} = 2[/tex]

Finally, the mass m can be found by

[tex]w = 4[/tex]

[tex]mg=4[/tex]

[tex]m = \frac{4}{g}[/tex]

Where g is approximately 32 ft/s²

[tex]m = \frac{4}{32} = \frac{1}{8}[/tex]

Therefore, the required differential equation is

[tex]my'' + \zeta y' + ky=0[/tex]

[tex]\frac{1}{8} y'' + 2y' + 24y=0[/tex]

The initial position is

[tex]y(0) = \frac{1}{2}[/tex]

The initial velocity is

[tex]y'(0) = 0[/tex]