Math Problem Statement

The cable AB has a diameter of 5.8 mm and has a Young's Modulus of 179. The cable must satisfy two conditions: the stress in the cable must be 203 MPa or less and the elongation must be 6.6 mm or less. What maximum load P is allowed? L = 5 m. State your answer in Newtons with 4 significant figures.

Solution

To solve this problem, we will address both the stress and the elongation conditions separately, and find the maximum allowable load PP that satisfies both conditions.

Given data:

  • Diameter of cable d=5.8mmd = 5.8 \, \text{mm}
  • Young's Modulus E=179GPa=179×109PaE = 179 \, \text{GPa} = 179 \times 10^9 \, \text{Pa}
  • Maximum stress σmax=203MPa=203×106Pa\sigma_{\text{max}} = 203 \, \text{MPa} = 203 \times 10^6 \, \text{Pa}
  • Maximum elongation ΔLmax=6.6mm=6.6×103m\Delta L_{\text{max}} = 6.6 \, \text{mm} = 6.6 \times 10^{-3} \, \text{m}
  • Length of cable L=5mL = 5 \, \text{m}

Step 1: Stress condition

The stress in the cable is given by the formula: σ=PA\sigma = \frac{P}{A} where:

  • σ\sigma is the stress,
  • PP is the load,
  • AA is the cross-sectional area of the cable.

The cross-sectional area of the cable is the area of a circle: A=π(d2)2=π(5.8×1032)2A = \pi \left( \frac{d}{2} \right)^2 = \pi \left( \frac{5.8 \times 10^{-3}}{2} \right)^2

The maximum stress is 203 MPa, so: σmax=PA\sigma_{\text{max}} = \frac{P}{A} Thus, the maximum allowable load due to stress is: Pstress=σmax×AP_{\text{stress}} = \sigma_{\text{max}} \times A

Step 2: Elongation condition

The elongation ΔL\Delta L of the cable is related to the load by Hooke's Law: ΔL=PLAE\Delta L = \frac{P L}{A E} Rearranging for PP: Pelongation=ΔLmaxAELP_{\text{elongation}} = \frac{\Delta L_{\text{max}} A E}{L}

Step 3: Calculation of PstressP_{\text{stress}} and PelongationP_{\text{elongation}}

1. Calculate the cross-sectional area AA:

A=π(5.8×1032)2=2.654×105m2A = \pi \left( \frac{5.8 \times 10^{-3}}{2} \right)^2 = 2.654 \times 10^{-5} \, \text{m}^2

2. Maximum load due to stress:

Pstress=203×106×2.654×105=5383.5NP_{\text{stress}} = 203 \times 10^6 \times 2.654 \times 10^{-5} = 5383.5 \, \text{N}

3. Maximum load due to elongation:

Pelongation=6.6×103×2.654×105×179×1095=7854.6NP_{\text{elongation}} = \frac{6.6 \times 10^{-3} \times 2.654 \times 10^{-5} \times 179 \times 10^9}{5} = 7854.6 \, \text{N}

Step 4: Determine the maximum allowable load

The maximum load PmaxP_{\text{max}} is the smaller of the two values, since both conditions must be satisfied: Pmax=min(Pstress,Pelongation)=min(5383.5,7854.6)=5383.5NP_{\text{max}} = \min(P_{\text{stress}}, P_{\text{elongation}}) = \min(5383.5, 7854.6) = 5383.5 \, \text{N}

Thus, the maximum allowable load is:

Pmax=5383.5NP_{\text{max}} = 5383.5 \, \text{N}

Final Answer:

The maximum load allowed is 5383.5 N.

Would you like further clarification or details on any of the steps? Here are a few related questions for exploration:

  1. How would the maximum load change if the diameter of the cable increased?
  2. How does Young's Modulus affect the elongation of the cable?
  3. What would happen if the maximum stress were increased beyond 203 MPa?
  4. How does the length of the cable affect its elongation for a given load?
  5. What is the relationship between force and stress in different materials?

Tip: When dealing with stress and elongation problems, always ensure the units are consistent across all calculations (e.g., convert diameters to meters, pressures to Pascals).

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Math Problem Analysis

Mathematical Concepts

Mechanics
Material Strength
Stress and Strain
Hooke's Law

Formulas

Stress: σ = P / A
Cross-sectional area of a circular cable: A = π(d/2)^2
Elongation: ΔL = (P * L) / (A * E)

Theorems

Hooke's Law
Stress-Strain Relationship

Suitable Grade Level

University Engineering Level