2.5 Archimedes Principle (Form 5)

Diagram below show an oil drum of volume V floating with 1/5 of its volume float on the surface of water. If the density of water is ρ, what is the buoyant force acting on the oil drum?

• 4/5 Vρg

• 1/5 Vρg

• Vρg

• 3/5 Vρg

State Archimedes' principle.

Answer explanation

Archimedes' principle state that an object which is partially of fully immersed in a fluid will experience a buoyant force equal to the weight of the fluid displaced.

Diagram 3.1 shows a metal block hanging from a spring balance while the diagram 3.2 shows the metal block immersed in Eureka can filled with water.

(i) What is the mass of the metal block?

Answer explanation

(a) m = W/g

= 8.0 /9.81

= 0.82kg

(b) Based on Diagram 3.2:

(i) What is the apparent loss in weight of the metal block?

Answer explanation

actual weight - apparent weight = apparent weight loss

8.0 N - 6.0 N = 2.0 N

(b) Based on diagram 3.2:

(ii) Explain why the spring balance shows a smaller reading

Answer explanation

There is buoyant force acting on a metal block.

Answer explanation