A rod of length l tapers uniformly from a diameter D at one end to a ...
To solve this problem, let's consider the elongation or extension of each rod separately.
For the first rod, which tapers uniformly from diameter D to D/2, we can assume that the tapering occurs linearly along the length of the rod. This means that the diameter changes uniformly from D to D/2, and therefore the cross-sectional area also changes uniformly.
Let's denote the original cross-sectional area of the rod as A₀ (corresponding to diameter D) and the cross-sectional area at any point along the length as A(x) (corresponding to diameter at that point).
Since the tapering is linear, we can express the cross-sectional area A(x) as a function of x, the distance from the end where the diameter is D. We can write:
A(x) = A₀ - (A₀ - Aₙ) * (x/l)
where Aₙ is the cross-sectional area at the other end of the rod (corresponding to diameter D/2) and l is the length of the rod.
Now, using Hooke's Law, we know that the stress (σ) in a rod is directly proportional to the strain (ε), which is the elongation divided by the original length. Mathematically, this can be written as:
σ = E * ε
where E is the Young's Modulus of elasticity.
Since the material and the axial load P are the same for both rods, the stress in both rods will be the same. Therefore, we can equate the stresses in the two rods:
E * ε₁ = E * ε₂
where ε₁ is the extension of the first rod and ε₂ is the extension of the second rod.
Now, we can calculate the extensions of the two rods using the formula for stress:
ε₁ = σ / E = P / (E * A₁)
ε₂ = σ / E = P / (E * A₀)
where A₁ is the cross-sectional area of the first rod, which can be calculated using the expression for A(x) as A(0) = A₀ and A(l) = Aₙ.
Now, substituting the expressions for A₁ and A₀ in terms of A₀ and Aₙ, we get:
ε₁ = P / (E * A₀)
ε₂ = P / (E * A₀)
Therefore, the ratio of the extension of the first rod to that of the second rod is:
ε₁ / ε₂ = (P / (E * A₀)) / (P / (E * A₀)) = 1
Hence, the correct answer is option 'd) 1'.
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