Find the maximum weight of a needle of length 4 cm that can float on water of surface tension 0.073 N/m.
Options

Question

Find the maximum weight of a needle of length 4 cm that can float on water of surface tension 0.073 N/m.

G1 Physics · Accepted Answer

Step 1: Surface tension acts along the two long contact lines of the floating needle. Step 2: The maximum upward surface-tension force is F = 2TL, assuming the maximum vertical component. Step 3: Convert length L = 4 cm = 0.04 m. Step 4: Fmax = 2 × 0.073 × 0.04 = 0.00584 N. Step 5: Equivalent mass m = Fmax/g ≈ 0.00584/10 = 5.84 × 10⁻⁴ kg = 0.584 g. Final answer: weight corresponding to 0.584 g (approximately 5.84 × 10⁻³ N); Option B.