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A metallic ring of radius 2 cm and cross-sectional area 4 cm² is fitted onto a wooden circular disc of radius 4 cm. If the Young's modulus of the ring material is 2 x 10¹¹ N/m², find the force with which the ring presses against (expands over) the disc.

1. 2 x 10⁷ N
2. 8 x 10⁷ N
3. 4 x 10⁷ N
4. 6 x 10⁷ N

Correct answer: 8 x 10⁷ N

Solution

Strain = (4 - 2)/2 = 1, so F = Y*A*strain = 2e11 * 4e-4 * 1 = 8 x 10⁷ N.

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