[د.امير]

Q2
We must figure out the raft’s weight and the buoyant force to stabilise the weight:
Given:
The density, of pine = 550 kg/m3
The volume of the wood = 4.0m*4.0m*0.30m=4.8m3 . Hence,
Weight of raft= (550 kg/m3)(4.8m3)(9.80 N/kg)=26 000 N.
When the raft is below surface level displacing 4.8 m3 of water, the maximum buoyant force exists and is equal to the weight of displaced water. Along with water’s density, it can be determined.
FB=Wfluid =(1000 kg/m3)(4.8 m3)(9.80 N/kg) = 47 000N
Since the maximum buoyant force is larger than the raft’s weight, then the raft will be afloat (Answer A).
B) the volume of the raft that will be beneath the water surface when
FB= Weight of raft = 26 000 N, or
FB= (1000 kg/m3) V (9.80 N/kg) = 26 000N, or
V = 2.65 m3
2.65 m3 = 4.0m*4.0m* t, where t is the depth of wood that will be beneath water,
t= 0.17m