Page 87 - Physics Form 5 KSSM_Neat

Example 2 CHAPTER 2

Photograph 2.8 shows a raft floating in the sea. The mass of the raft is 54 kg and the density of sea Pressure
water is 1 080 kg m .
–3
[Gravitational acceleration, g = 9.81 m s ]
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(a) What is the weight of the raft?
KEMENTERIAN PENDIDIKAN MALAYSIA
(b) Compare the weight of the raft with the weight of
sea water displaced.
(c) Calculate the volume of water displaced by the raft.

Solution Photograph 2.8 Raft

(a) Weight of raft, W (b) The raft is in equilibrium
Mass of raft, m = 54 kg Weight of raft = buoyant force
Gravitational acceleration, g = 9.81 m s –2 According to Archimedes’ principle,
W = mg buoyant force = weight of water displaced
= 54 × 9.81 Therefore,
= 529.74 N weight of raft = weight of sea water displaced
(c) Volume of water displaced, V
Weight of raft, W = 529.74 N
Density of sea water, ρ = 1 080 kg m –3
Weight of raft = weight of sea water displaced
W = ρVg
529.74 = 1 080 × V × 9.81
529.74
V =
1 080 × 9.81
= 0.05 m 3

Formative Practice 2.5

1. State Archimedes' principle.

2. A small boat displaces 3.8 × 10 m of sea water. Calculate the buoyant force acting on
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3
the boat.
[Density of sea water, ρ = 1 050 kg m and gravitational acceleration, g = 9.81 m s ]
–2
–3
3. Figure 2.42 shows a block of mass 0.48 kg and volume
–4
5.0 × 10 m being held in water. The density of water
3
–3
is 1 000 kg m . Determine the movement of the block
when it is released.
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[Density of water, ρ = 1 000 kg m and Block
–2
gravitational acceleration, g = 9.81 m s ]
Figure 2.42
LS 2.5.4 77