Question

19 The predominant mode of heat transfer in solids is -----------
convection
conduction
radiation
diffusion

20 A piece of plastic barely floats in water. If it has a mass of 20g, what is its volume?
30cm3
20cm3
10cm3
2cm3

Answer 1

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Answer on Question #58130, Physics / Mechanics | Relativity |

19 The predominant mode of heat transfer in solids is ---

convection

conduction

radiation

diffusion

Solution:

Conduction is the most significant means of heat transfer within a solid or between solid objects in thermal contact.

Answer: conduction

20 A piece of plastic barely floats in water. If it has a mass of 20g, what is its volume?

30cm³

20cm³

10cm³

2cm³

Solution:

Newton's second law for the piece of plastic on Y-axis:

$$m g - F _ {A} = 0$$

The Archimedes force is

$$F _ {A} = \rho g V$$

where $\rho = 1\mathrm{g / cm}^3$ is density of water.

$$m g - \rho g V = 0$$

Thus,

$$V = \frac {m}{\rho} = \frac {20}{1} = 20 \mathrm{~cm} ^ {3}$$

Answer: $20~\mathrm{cm}^3$