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A gold sphere of a given size falls through a viscous liquid and attains a terminal speed of 0.2 m/s. If the gold has density 19.5 kg/m³ and the liquid has density 1.5 kg/m³, what terminal speed will a silver sphere of the same size have in the same liquid, given that silver has density 10.5 kg/m³?

1. 0.4 m/s
2. 0.133 m/s
3. 0.1 m/s
4. 0.2 m/s

Correct answer: 0.1 m/s

Solution

For the same size and liquid, v is proportional to (rho_sphere - rho_liquid). v_silver = 0.2 * (10.5 - 1.5)/(19.5 - 1.5) = 0.2 * 9/18 = 0.1 m/s.

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