A 7.8 kg object starting from rest falls through a viscous medium and experiences a resistive force R = −b v, where v is the velocity of the object. The acceleration of gravity is 9.8 m/s 2 . If the object’s speed reaches one-half its terminal speed in 6.56 s, determine the terminal speed.

Respuesta :

Answer:

The terminal voltage is [tex]v_T = 90.76\ m/s[/tex]

Explanation:

From the question we are given that the Resistive force R is mathematically represented as

                    [tex]R = -bv[/tex]

       Where b is a constant  known as drag coefficient

          v is the velocity of the object

The objective of this solution is to obtain the terminal speed and this is mathematically represented as

                          [tex]V_T = \frac{mg}{b}[/tex]

 Where  m is the mass

               g acceleration due to gravity

       

As the time changes the velocity of the object change and this can be mathematically represented as

                             [tex]v = v_T[1-e^{bt/m}][/tex]

We are told that the  [tex]v = \frac{1}{2} v_T \ at \ t = 6.56s[/tex]

              So substituting this into the above equation we have

                                 [tex]\frac{v_T}{2} = v_T [1-e^{bt/m}][/tex]

                                     [tex]\frac{1}{2} = 1- e^{bt/m}[/tex]

                    [tex]e^{-(b*6.56)/m}= 1-\frac{1}{2}[/tex]

                              [tex]\frac{b}{m} = \frac{ln(2) }{6.56}[/tex]

Substituting  m = 7.8 kg

                           [tex]b= \frac{ln(2)}{6.56} *7.8 =0.8242\ kg/m[/tex]

Now substituting this value to get the terminal velocity we have

                        [tex]v_T = \frac{7.8 * 9.8}{0.8422} =90.76\ m/s[/tex]

The terminal speed of the given object could be stated as:

[tex]90.76 m/s[/tex]

Given that,

R(Resistive Force) [tex]= -bv[/tex]

where [tex]b[/tex] being constant and [tex]v[/tex] represents the velocity

To find,

Terminal speed = ?

We will represent terminal speed as [tex]v_{T}[/tex].

so,

[tex]v_{T}[/tex] [tex]= mg/b[/tex]

where [tex]m[/tex] represents mass and

[tex]g[/tex] represents acceleration due to gravity.

With the alteration in time, the velocity varies as well. Therefore,

[tex]v_{T}/2 = v_{T}[1 - e^{bt/m}][/tex]

As we know,

[tex]v = 1/2v_{T}[/tex] and t = 6.56s

After putting these values in [tex]v_{T}/2 = v_{T}[1 - e^{bt/m}][/tex], we get

[tex]b = \frac{In(2)}{6.56}[/tex] × [tex]7.8[/tex]

[tex]= 0.8242 kg/m[/tex]

After this, we will put b's value in the former equation,

[tex]v_{T}[/tex] [tex]= (7.8[/tex] × [tex]9.8)/0.8242[/tex]

∵ [tex]v_{T}[/tex] [tex]= 90.76 m/s[/tex]

Thus, [tex]90.76 m/s[/tex] would be characterized as the terminal speed.

Learn more about "Terminal Speed" here:

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