8.1.8 Buoyancy and Archimedes' Principle

Question 1

Buoyancy and Archimedes’ Principle

Answer 1

• The net force that a fluid exerts on a submersed object is called the buoyant force. Archimedes’ principle states that the buoyant force on an object is given by the formula .
• An object will sink if its density is greater than the density of the fluid in which it is immersed

Question 2

The weight of an object is
W = m0g = P0V0g
Based on Archimedes’ principle, the weight of the volume of fluid the object displaces is: Fb = PfVfg (where Vf is the volume of fluid displaced). If the object is completely submerged in a liquid, Vo = Vf. Dividing the second equation by the first gives Fb/Wo = Pf/Po. Thus the buoyant force is Fb = Pf/Po*Wo. Which of the following is not correct?

Answer 2

The buoyant force on an object rising in the atmosphere is constant.

Question 3

A metal box of dimensions 40.0 cm × 22.0 cm × 35.0 cm is partially under water. Its total height is 35.0 cm and 5.0 cm of its height is floating above water. Which of the following is the buoyant force exerted on the box by the water? Use 1000 kg / m3 for the density of water.

Answer 3

258.7 N

Question 4

The density of air is 1.25 kg / m3. Few objects float in air, however, a hot-air balloon is a familiar example. Which of the following statements concerning hot-air balloons is not correct?

Answer 4

A hot-air balloon can lift more on a hot day than on a cold day.

Question 5

Which of the following statements concerning buoyancy is not correct?

Answer 5

The net upward or downward force exerted on an object is called the buoyant force.

Question 6

Which of the following statements about Archimedes’ principle is incorrect?

Answer 6

Because pressure in a liquid is greater at a greater depth, the buoyant force depends on depth in the liquid.

Question 7

Wood and ice both float in water. Ice floats because its density is 92% of the density of water. Consider the case of wooden block that is 80% of the density of ice. What percentage of this piece of wood will be above the surface of water as it floats?

Answer 7

26.4 %

Question 8

True or false?
Archimedes’ principle states that a body immersed in a fluid is buoyed up by a force equal in magnitude to the weight of the volume of fluid it displaces.

Answer 8

true

Question 9

A piece of metal is placed in a series of liquids. The liquids have sequentially greater density. The buoyant force of the liquid on a cubic foot of the submerged metal ____________.

Answer 9

increases

Question 10

A series of solids are manufactured so that they increase in density by a constant amount. The solids are consecutively placed into a tub of water starting with the least dense and ending with the most dense. As the density of the solids increases, the buoyant force of water on a cubic foot of the submerged solid _____________.

Answer 10

remains the same