Trang 4/6 - Mã đề thi 248
Read the following passage and mark the letter A, B, C, or D on your answer sheet to indicate the
correct answer to each of the questions from 46 to 55.
Archimedes' Principle is a law of physics that states that when an object is totally or partially
immersed in a fluid, it experiences an upthrust equal to the weight of the fluid displaced. The
principle is most frequently applied to the behaviour of objects in water, and helps to explain floating
and sinking, and why objects seem lighter in water. It also applies to balloons.
The key word in the principle is “upthrust”, which refers to the force acting upward to reduce the
apparent weight of the object when it is under water. If, for example, a metal block with a volume of
100 cm3 is dipped in water, it displaces an equal volume of water, which has a weight of
approximately 1 N (3.5 oz). The block therefore seems to weigh about 1 N less.
An object will float if its average density is less than that of water. If it is totally submerged, the
weight of the water it displaces (and hence the upthrust on it) is greater than its own weight, and it is
forced upward and out of the water, until the weight of the water displaced by the submerged part is
exactly equal to the weight of the floating object. Thus a block of wood with a density six tenths that
of water will float with six tenths of its volume under water, since at that point the weight of fluid
displaced is the same as the block’s own weight. If a dense material is made into a suitable shape, it
will float because of Archimedes’ principle. A ship floats, whereas a block of iron of the same mass
sinks.
It is also because of Archimedes’ principle that ships float lower in the water when they are
heavily loaded (more water must be displaced to give the necessary upthrust). In addition, they cannot
be so heavily loaded if they are to sail in fresh water as they can if they are to sail in the sea, since
fresh water is less dense than sea water, and so more water must be displaced to give the necessary
upthrust. This means the ship is lower in the water, which can be dangerous in rough weather.
From "Archimedes' Principle", Microsoft® Student 2008 [DVD]. Microsoft Corporation, 2007.
Question 46: What happens when something is immersed in a fluid?
A. It will be pushed further down with a force, equal to the weight of the fluid displaced.
B. It receives an upward force, equal to the weight of the fluid displaced.
C. It receives a downward force, equal to the weight of the fluid displaced.
D. The fluid will expand the object and overflow to the floor.
Question 47: The word “volume” in the passage refers to ______.
A. loudness B. quantity C. frequency D. length
Question 48: The word “displaces” in the passage almost means “______”.
A. takes the place of B. takes place
C. replaces with a new one D. puts in position
Question 49: If an object’s average density is less than that of water, the object will ______.
A. sink B. float C. inflate D. drift
Question 50: A block of wood with a density seven tenths that of water will ______.
A. go up and down then sink
B. float with a half of its volume under water
C. float with an equal volume of its volume under water
D. sink immediately when submerged
Question 51: A ship floats, whereas a block of iron of the same mass sinks because the ship ______.
A. is made of wood B. is lighter C. has buoys D. has a special shape
Question 52: The phrase “six tenths” in the passage means “______”.
A. 6 and 10 B. 10/6 C. 10 of 6 D. 6/10
Question 53: The word “upthrust” in the passage refers to the ______.
A. upward push B. upper side of an object
C. upturned force D. upside-down turn
Question 54: Ships cannot be so heavily loaded if they want to sail in fresh water as they sail in the
sea, because ______.
A. fresh water is ‘lighter’ than sea water B. there’s too much salt in sea water
C. sea water is ‘saltier’ than fresh water D. fresh water is more polluted
Question 55: Archimedes' Principle explains why ______.
A. all objects will float B. Archimedes became famous
C. objects seem lighter in water D. humans can swim