Max (mass = 15 kg) is hanging from one end of a 13-m long bungee cord that has its other end fixed to a bridge above. The bungee cord has a circular cross section with a diameter of 2.5 cm, and a Young’s modulus of 17 MPa. What is the stress in the bungee cord due to Max’s weight?

Respuesta :

The stress in the bungee cord due to the Max's weight is [tex]\fbox{\begin \\ 299511\text{ N}/\text{m}^{2}\end{minispace}}[/tex] or [tex]\fbox{\begin\\ 2.99\times10^{5}\text{ N}/\text{m}^{2}\end{minispace}}[/tex] or [tex]\fbox{\begin\\3.0\times10^{5}\text{ N}/\text{m}^{2}\end{minispace}}[/tex].

Further Explanation:

The stress developed in the bungee cord is the amount of tensile force developed inside the bungee cord due to the Max's weight.

Given:  

The diameter d of the bungee cord is [tex]2.5\text{ cm}[/tex].  

The mass m of Max is [tex]15\text{ kg}[/tex].

Concept:

The stress developed in the bungee cord is given by:  

[tex]\fbox{\begin \sigma =\dfrac{F}{A}\end{minispace}}[/tex]                                                                               ... (1)         

Here, [tex]\sigma[/tex] is the stress developed in the bungee cord, [tex]F[/tex]is the force due to Max's weight and [tex]A[/tex] is the area of cross-section of the bungee cord.  

The radius of the bungee cord will be the half of its diameter.  

[tex]r=\dfrac{d}{2}[/tex]

Substitute [tex]2.5\text{ cm}[/tex] for [tex]d[/tex].  

[tex]r= \dfrac{2.5\text{ cm}}{2}\\r=1.25 \text{ cm}[/tex] 

Convert the radius of the bungee cord in meter.  

[tex]r=\dfrac{1.25}{100} \text{ m}\\r=0.0125\text{ m}[/tex] 

The area of cross-section of the bungee cord is given by:  

[tex]A=\pi r^{2}[/tex]  

Substitute [tex]0.0125\text{ m}[/tex] for [tex]r[/tex].  

[tex]A=\pi (0.0125\text{ m})^{2}\\A=4.908\times10^{-4} m^{2}[/tex]  

The force on the bungee cord due to Max's mass is the gravitational force acting on Max's body. The gravitational force acting on Max's body is given by:  

[tex]F=mg[/tex]  

Here, m is the mass of Max's body and g is acceleration due to gravity.  

Consider the value of acceleration due to gravity on Earth be [tex]9.80\text{ m}/\text{s}^{2}[/tex].  

Substitute [tex]15\text{ kg}[/tex] for m and [tex]9.80\text{ m}/\text{s}^{2}[/tex] for g in above expression.  

[tex]F=(15\text{ kg})\times(9.80\text{ m}/\text{s}^{2})\\F=147\text{ N}[/tex]  

Substitute [tex]147\text{ N}[/tex] for F and [tex]4.980\times10^{-4}\text{ m}^{2}[/tex] for A in equation (1).  

[tex]\sigma=\dfrac{147\text{ N}}{4.908\times10^{-4}\text{ m}^{2}}\\\sigma=299511\text{ N}/\text{m}^{2}[/tex]

Thus, the stress developed in the bungee cord is [tex]\fbox{\begin \\ 299511\text{ N}/\text{m}^{2}\end{minispace}}[/tex] or [tex]\fbox{\begin\\ 2.99\times10^{5}\text{ N}/\text{m}^{2}\end{minispace}}[/tex] or [tex]\fbox{\begin\\3.0\times10^{5}\text{ N}/\text{m}^{2}\end{minispace}}[/tex].

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Answer Details:

Grade: Senior school

Subject: Physics

Chapter: Stress and Strain

Keywords:

Max, Max's weight, force, stress, area, 299511 N/m2, 299511 N/m^2, 2.99x10^5 N/m2, gravitational, radius, bungee, cord, weight, developed, mass, 3x10^5 N/m^2.

Ver imagen Adityasonisds

The stress in the bungee cord due to Max’s weight is 294,000 N/m².

The given parameters;

  • mass of Max, m = 15 kg
  • diameter of the cord, d = 2.5 cm
  • radius of the cord, r = = 1.25 cm = 0.0125 m
  • Young's modulus of the rod, E = 17 MPa

The area of the bungee cord is calculated as follows;

[tex]A = \pi r^2\\\\A = \pi \times (0.0125)^2\\\\ A= 0.0005 \ m^2[/tex]

The weight of Max is calculated as follows;

[tex]F = mg\\\\F = 15 \times 9.8\\\\F = 147 \ N[/tex]

The stress in the bungee cord due to Max’s weight is calculated as;

[tex]\sigma = \frac{F}{A} \\\\\sigma = \frac{147}{0.0005} \\\\\sigma = 294,000 \ N/m^2[/tex]

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