Question:

A horizontal metal rod of diameter 4 cm projects 6 cm from a wall. The shear modulus of the metal is \(3 \times 10^{10}\, N\,m^{-2}\). An object of mass 1100 kg is suspended from the free end of the rod. The free end of the rod moves down by a distance. (Take \(g = 10\,m\,s^{-2}\), neglect mass of rod)

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For shear problems, always use \( \Delta x = \frac{FL}{AG} \) and carefully track powers of 10 in area.
Updated On: Jun 19, 2026
  • \(2.5 \times 10^{-6}\, m\)
  • \(6.75 \times 10^{-5}\, m\)
  • \(2.25 \times 10^{-6}\, m\)
  • \(1.75 \times 10^{-5}\, m\)
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The Correct Option is D

Solution and Explanation

Step 1: Identify given parameters.
Diameter \(d = 4\,cm = 0.04\,m\), so radius \(r = 0.02\,m\).
Length \(L = 6\,cm = 0.06\,m\).
Shear modulus \(G = 3 \times 10^{10}\,N\,m^{-2}\).
Force \(F = mg = 1100 \times 10 = 11000\,N\).

Step 2: Use shear strain formula.

For lateral displacement: \[ \Delta x = \frac{FL}{AG} \]

Step 3: Area of cross-section.

\[ A = \pi r^2 = \pi (0.02)^2 = 1.256 \times 10^{-3}\,m^2 \]

Step 4: Substitute values.

\[ \Delta x = \frac{11000 \times 0.06}{(1.256 \times 10^{-3})(3 \times 10^{10})} \]

Step 5: Simplify.

Numerator: \[ 11000 \times 0.06 = 660 \]
Denominator: \[ 3.768 \times 10^{7} \]

Step 6: Final result.

\[ \Delta x \approx 1.75 \times 10^{-5}\,m \]
Final Answer: \[ \boxed{1.75 \times 10^{-5}\,m} \]
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