Pressure

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Pressure (O Level)

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Question 1
A column of liquid X floats on water in a U-tube of uniform cross-section area. If the density of water is 1000 kg m-3, find the density of liquid X (in kg m-3). 1
A
1500
B
1000
C
800
D
500
Question 1 Explanation: 
h w X p w X g = h x X p x X g p x = (h x X p w)/h x = (0.1 x 1000) / 0.2 = 500 kg m^3
Question 2
The diagrams below show a V-shaped object placed in different orientations. In which position does the object exert the maximum pressure on the surface it is resting? 2
A
A
B
B
C
C
D
D
Question 2 Explanation: 
Maximum pressure is exerted if the contact area is minimum.
Question 3
On a cloudy day , a sealed packet of potato chips is taken to the top of a mountain. The packet is found to be blown up like a baloon. This could be because
A
the air outside the packet is hotter than the air inside the packet.
B
the air outside is now at a lower pressure than the air inside the packet.
C
the ultraviolet radiation has increased.
D
the packet has a small hole that allowed air to leak in.
Question 3 Explanation: 
At the top of the mountain, the external pressure is low.
Question 4
In the diagram below a person of mass 50 kg is standing on a platform over the piston of area 2.0 x 10-2 m2. What height of water h will just support her? Assume that the density of water is 1000 kg m-3. 4
A
0.25 m
B
2.5 m
C
5.0 m
D
10 m
Question 4 Explanation: 
F / A = hpg h = F / (Apg) = 500 / (2.0 x 0.01 x 1000 x 10) =2.5 m
Question 5
The diagrams below show 4 mercury barometers. In which of these is the external pressure greatest? 5
A
A
B
B
C
C
D
D
Question 5 Explanation: 
External pressure on a fluid is independent of cross-sectional area. The higher the height of the barometer, the higher is the external pressure.
Question 6
The apparatus in the diagram below is set up at a constant temperature of 20oC, d=12 cm, h=10 cm. Air is trapped inside the left handed closed limb while the right-hand limb can be moved up & down. The atmospheric pressure is 760 mm Hg. If the right-hand limb is raised such that h is 15 cm, what is the length of the trapped air, d ? 6
A
8.0 cm
B
11.3 cm
C
11.9 cm
D
17.0 cm
Question 6 Explanation: 
P1V1 = P2V2 860 x 12 = 910 x h2 h2 = (860 x 12) / 910 = 11.3 cm
Question 7
Oxygen is compressed in the sealed end of a long J-tube by means of a column of mercury open to the atmosphere as shown. Mercury has density of 13.6 x 103 kg m-3 and the atmospheric pressure is 1.01 x 103 Pa. What is the atmospheric ratio of the pressure of oxygen to that of the atmosphere?
A
1.5 : 1
B
2.0 : 1
C
2.5 : 1
D
3.0 : 1
Question 7 Explanation: 
P0 = hm x pm x g + Patm = (1.52 x 13.6 x 1000 x 10) + (1.01 x 100000) = 3.07 x 100000 P0 : Patm = 3 : 1
Question 8
The surface of water in a domestic tank is 6 m above a cold water tap. The density of water is 1000 kg m-3. What is the pressure of water as it leaves the tap?
A
60 Pa
B
600 Pa
C
6000 Pa
D
60000 Pa
Question 8 Explanation: 
P = hpg = 6 x 1000 x 10 = 60000 Pa
Question 9
The pressure produced by a cubic block is P. Find the pressure if length l is double.
A
P/4
B
P/2
C
2P
D
4P
Question 9 Explanation: 
Ps = F/A Pb = mg/A = mg/A = pVg/A = pVg/A = p8l^3g / 4l^2 = pl^3g / l^2 = 2plg = plg = 2Ps
Question 10
The following diagram shows a barometer containing a liquid of density 1200 kg m-3 above the mercury column. If the atmospheric pressure is 76 cm Hg than the height of the liquid in cm is ( Given that the density of mercury is 13600 kg m-3) 10
A
22.7
B
2
C
26
D
76
Question 10 Explanation: 
Patm = Pm + P1 0.76 x 13600 x 10 = (0.74 x 13600 x 10) + (h x 1200 x 10) h = 0.227 m = 22.7 cm
Question 11
Some air is trapped in the space above the mercury in a barometer. Let l be the height of the air column trapped and h be the height of the mercury column. When the glass tube is pressed down into the mercury bath, which of the following best describes the change of l and h? 11  
A
l h Decrease Remain
B
Remain Decrease
C
Decrease Decrease
D
Decrease Increase
Question 11 Explanation: 
As l decreases, the trapped air exerts a greater pressure. As the pressure due to the increased trapped air together with the decreased pressure due to the mercury column give the value of the constant atmospheric pressure.
Question 12
The diagram below shows a simple mercury barometer. Which of the following does NOT cause the height of the mercury column to vary? 12
A
Changes in atmospheric pressure
B
Changes in the value of g
C
Changes in the temperature of mercury
D
Evaporation of Mercury from the barometer reservoir.
Question 12 Explanation: 
The amount of mercury in the reservoir does not cause the mercury column to vary.
Question 13
The diagram shows a mercury column in a test tube supported by the atmosphere. What is the pressure of the gas given that the atmospheric pressure is 76 cm Hg? 13
A
81 cm Hg
B
76 cm Hg
C
71 cm Hg
D
0 cm Hg
Question 13 Explanation: 
Pgas + PHg = Patm Pgas = Patm - PHg = 76 - 5 = 71 cm Hg
Question 14
A rectangular block weighing 192 N has dimensions 8 cm x 6 cm x 2 cm. What is the maximum pressure it can exert when it is placed on a horizontal surface?
A
40000 Pa
B
120000 Pa
C
160000 Pa
D
200000 Pa
Question 14 Explanation: 
P = F / A (The smaller the cross-sectional area, the higher the pressure.) = 192 / (0.06 x 0.02) = 16 x 10000 Pa
Question 15
The handle of the piston below was initially at the 5 cm mark (dotted line). Assuming that the temperature of the air inside the cylinder is constant and that no air is able to escape from the cylinder, what is the pressure in the cylinder if the piston is pulled to the 20 cm mark as shown below? 15
A
Four times its initial pressure
B
Three times its initial pressure
C
Reduced to a third of its initial pressure
D
Reduced to a quarter of its initial pressure
Question 15 Explanation: 
P is inversely proportional to V
Question 16
A flask is filled with air and tightly stoppered at room temperature. The flask is then placed in melting ice. The flask stays the same size. In the flask, what happens to the pressure of the air and the speed of the molecules in the air? 16
A
Pressure Speed of Molecules Decrease Increase
B
Increase Increase
C
Decrease Decrease
D
Increase Decrease
Question 16 Explanation: 
When the temperature is decreased, the speed of the molecules will decrease. When teh speed decreases, the molecules make fewer collisions with the walls of the container.
Question 17
The first diagram on the left shows a simple barometer in its original state. The next four diagrams show the barometer after something has been done to it. Which of the following diagrams A, B, C, D is correct? 17
A
A
B
B
C
C
D
D
Question 17 Explanation: 
The height of the mercury column must be the same.
Question 18
The mercury barometer shown below contains some trapped air in the tube. If the atmospheric pressure is 75 cm Hg, what is the pressure exerted by the trapped air? 18
A
5 cm Hg
B
10 cm Hg
C
15 cm Hg
D
20 cm Hg
Question 18 Explanation: 
The pressure due to the mercury column together with the pressure due to the trapped air, will give the value of the atmospheric pressure.
Question 19
Two solid cubes are made from the same material . One cube has sides that are 2 times as long as the other. When placed on one side, the small cube exerts a pressure p on the ground. If one area of each side of the small cube is A, determine the pressure exerted by the large cube standing on one of its faces. 19
A
2p
B
4p
C
8p
D
13p
Question 19 Explanation: 
Ps = F/A Pb = mg/A = mg/A = pVg/A = pVg/A = p8s^3g / 4s^2 = pws^3g / s^2 = 2psg = psg = 2Ps
Question 20
A forked tube contains air in one branch and a vacuum in the other as shown. The pressure of the enclosed air is 20
A
k cm Hg
B
d cm Hg
C
(h - k) cm Hg
D
(h - d) cm Hg
Question 21
Four mercury barometers of different cross-section areas have been set up to measure the atmospheric pressure at different places. Which place has the lowest atmospheric pressure? 21
A
A
B
B
C
C
D
D
Question 21 Explanation: 
The pressure measured is independent of the cross-sectional area but dependent on height of mercury column.
Question 22
The diagram shows a simple mercury barometer inclined at 60o to the horizontal. The atmospheric pressure in cm in Hg is 22
A
27.4
B
75.2
C
69.3
D
80.0
Question 22 Explanation: 
Vertical Height = 80 sin 60 deg = 69.3 cm
Question 23
The diagram shows a water manometer made form wide glass tubing and is designed to compare the pressure of two gases P & Q. Which of the following statements is true? 23
A
If the pressure of gases P & Q were equal, the meniscus at Y would move down 8 cm.
B
The pressure of gas Q is greater than the pressure of gas P by a column of water of height 8 cm.
C
The pressure of gas P is greater than the pressure of gas Q by a column of water of height 8 cm.
D
The maximum pressure difference that this manometer can measure is equal to a column of water of height 12 cm.
Question 23 Explanation: 
The pressure due to gas P is greater than gas Q. The difference in levels gives the difference in pressure value.
Question 24
The diagram below shows a pipette filler used to fill up a pipette with acid. Which of the following statements is true? 24
A
Po is a vacuum
B
Po has same pressure as the atmosphere
C
When the nozzle X is pressured lightly, the liquid level falls because the pressure in Po increases.
D
If the surrounding atmospheric pressure suddenly decreases, the liquid level will not change.
Question 25
A building is 512 m high. What must be the minimum water pressure in a pipe at ground level in order to get water up to a restaurant on the top floor? (Density of water - 1000 kg m-3, acceleration due to gravity = 10 m s-2)
A
1 x 10^5 Pa
B
5 x 10^6 Pa
C
6 x 10^5 Pa
D
5 x 10^8 Pa
Question 25 Explanation: 
P = hpg = 512 x 1000 x 10 = 5.12 x 10^6
Question 26
When a barometer is taken up a balloon, the mercury level
A
falls, because air pressure increases with height
B
falls, because air pressure decreases with height
C
rises, because air pressure increases with height
D
rises, because air pressure decreases with height
Question 27
The diagram shows a water manometer with one end connected to the gas tap and the other end left open. If the pressure of the gas increases by a value equivalent to x m of water pressure and atmospheric pressure, P decreases by a value equal to y m of water pressure, the value of G will be increased by 27
A
(x + y) m
B
(x - y) m
C
2(x + y) m
D
(y - x) m
Question 28
Diagram 1 shows a J-shaped tube containing 3.0 cm3 of air trapped by mercury. The mercury levels are the same on both sides of the tube. More mercury is poured into the open tube until the levels differ by 76 cm, as shown in diagram 2. The atmospheric pressure remains constant at 76 cm of mercury. 28
A
0.50 cm^3
B
0.67 cm^3
C
1.0 cm^3
D
1.50 cm^3
Question 28 Explanation: 
P is inversely proportional to V P1 / P2 = V2 / V1 P / 2P = V2 / 3 V2 = 1.5 cm^3
Question 29
The diagram shows a bubble at the bottom of a pool. Assuming that the temperature of the pool is constant throughout the water, which of the following describes the change of the pressure and the density of air in the bubble as it rises to the surface? 29   Pressure                        Density
A
Increase Increase
B
Increase Decrease
C
Decrease Increase
D
Decrease Decrease
Question 29 Explanation: 
As the bubble rises to the surface, the pressure felt by the bubble decreases. As such the fixed amount of air within the bubble would have to occupy a bigger volume in order for the pressure to decrease. D = M/V. As the volume increases, and mass remains constant, the density will decrease.
Question 30
Diagram 1 represents a mercury-filled simple barometer as would be used to measure atmospheric pressure. Diagram 2 shows the same barometer after a volatile liquid has been introduced on top of the mercury and a small quantity can be seen on top of the mercury. The saturated water vapour pressure of the liquid, in terms of the length of mercury column, is 30
A
W + Y
B
Y
C
Z + X
D
Z - X
Question 31
The diagram shows a mercury barometer on a day when the atmospheric pressure is 750 mm Hg. What is the pressure at point P at the bottom of the mercury column? 31
A
0 mm Hg
B
150 mm Hg
C
750 mm Hg
D
900 mm Hg
Question 31 Explanation: 
The pressure at point P is (750 + 150) = 900 mm Hg
Question 32
As a hydrogen balloon rises from the ground level to an altitude of 300 m, its volume increases. Which pressure changes have occurred within the balloon and the air outside the balloon? 32             Pressure change                         Pressure change in the balloon                               of air outside
A
Decrease Decrease
B
Decrease Increase
C
Increase Decrease
D
Increase Increase
Question 32 Explanation: 
As the balloon rises, the atmospheric pressure decreases. The balloon expands so that the fixed amount of hydrogen molecules within the balloon, now occupies a bigger volume. Thus the pressure within the balloon decreases to match the external pressure.
Question 33
A forked tube contains air in one branch and a vacuum in the other. The pressure of the enclosed air in mm Hg is 33
A
50
B
150
C
200
D
600
Question 34
A balloon filled with Helium was released from the bottom of a tall building at sea level. At the bottom of the building, the balloon had a volume of 500 cm3, while at the top, the volume was found to be 510 cm3. The pressure at sea level is 1,00,000 Pa. If the density of air is 1.29 kg m-3, what is the height of the building?
A
126 m
B
132 m
C
152 m
D
760 m
Question 34 Explanation: 
P1V1 = P2V2 500 x 100000 = 510 x (100000 - h x 1.29 x 10) h = 152 m
Question 35
A height of 0.81 m of a column of a turpentine exerts the same amount of pressure as a heavy box of weight of 68,040 N. The base area of the box is 10 m2. What is the density of turpentine in kg m-3?
A
8400
B
6804
C
1000
D
840
Question 36
The pressure of the water near the bottom of the wall forming a dam to a reservoir does not depend on __________.
A
the depth of the water
B
the cross sectional area of the reservoir
C
density of water
D
atmospheric pressure
Question 36 Explanation: 
The pressure due to a fluid is independent of the cross-sectional area of the fluid.
Question 37
The diagram shows a column of air enclosed in a narrow capillary tube by a thread of mercury 12 cm in length.  What is the pressure on the trapped air, given that the atmospheric pressure is 76 cm Hg? 37
A
12 cm Hg
B
64 cm Hg
C
76 cm Hg
D
88 cm Hg
Question 37 Explanation: 
Pair + PHg = Patm Pair = 76 - 12 = 64 cm Hg
Question 38
The diagram below shows a simple hydraulic jack. Which of the following changes will enable heavier loads to be lifted? 38 Diameter of W                         Diameter of Z
A
Doubled Remains the same
B
Doubled Halved
C
Remains the same Halved
D
Halved Doubled
Question 38 Explanation: 
When the diameter of W is halved, the pressure exerted is big. This pressure is transmitted to the piston Z. By having a big diameter for piston Z, the force is large.
Question 39
The diagram below shows a simple mercury barometer. To find the atmospheric pressure the vertical distance is measured betweeen ____________. 39
A
P and R
B
Q and R
C
Q and S
D
P and S
Question 40
the diagram shows the water levels in a water manometer used to measure the pressure of a gas supply. How much greater than the atmospheric pressure is the pressure of the gas supply? 40
A
2 cm of water
B
5 cm of water
C
10 cm of water
D
12 cm of water
Question 40 Explanation: 
The pressure of the gas supply is measured by the difference of the water levels = 15 - 5 = 10 cm of water.
Question 41
Which of the following depends on the atmosphere exerting pressure?
A
A ball falling to the ground
B
Drinking through a straw
C
The spray from a can cola
D
Bath water emptying down a plug hole
Question 42
A piston of negligible weight encloses air in a cylinder as shown. The air expands and the piston moves 4 cm upwards. What will be the pressure of the air inside? (Atmospheric pressure of air inside is 100 kPa.) 42
A
25 kPa
B
50 kPa
C
75 kPa
D
100 kPa
Question 42 Explanation: 
P is inversely proportional to V. P1/P2 = V2 / V1 P / 100 = 12 / 16 P = 12 / 16 x 100 = 75 kPa
Question 43
Water is contained in a container of base area A1, up to height h1. Water is also contained in a second container of bigger base area A2, but up to a smaller height h2. The hydrostatic pressure exerted on base A1 is P1 whiles that exerted on base A2 is P2. Which of the following statements is correct? 43
A
It is possible that P1 = P2 since A2 > A1 and h1 > h2
B
P1 < P2 because A2 > A1
C
P1 > P2 because A2 > A1
D
P1 > P2 because h1 > h2
Question 43 Explanation: 
Pressure due to a fluid independent of cross-sectional area; it is proportional to the height of the fluid.
Question 44
              44           The diagram above shows a manometer is connected to a gas supply. The liquid levels on both limbs of the manometer rise to a height difference of h. What changes would make the value of h larger?
A
Increase the cross sectional area of the limbs
B
Use another liquid which has a lower density
C
Use another liquid which has a higher density
D
Carry out the experiment on a planet which a stronger gravity
Question 44 Explanation: 
If another liquid of lower density is used, the height difference would be larger to indicate the same pressure difference since P = hpg.
Question 45
In one minute, a deep-sea diver breathes 1 litre of air at an atmospheric pressure of 100 kPa. At a certain depth in the sea, the pressure os the air supply is 300 kPa. To breathe in the same mass of air in one minute, what volume of air would he need?
A
1/3 litre
B
1/2 litre
C
1 litre
D
3 litres
Question 45 Explanation: 
P is inversely proportional to V P1 / P2 = V2 / V1 100 / 300 = V2 / 1 V2 = 1/3 litre
Question 46
The diagrams below show air trapped in a capillary tube by a small mercury plug. The length of the mercury plug is 10 cm. The atmospheric pressure is 76 cm Hg. The pressure of the trapped column of air in I & II is given by 46   Diagram I                          Diagram II
A
10 cm Hg 76 cm Hg
B
10 cm Hg 86 cm Hg
C
76 cm Hg 10 cm Hg
D
76 cm Hg 86 cm Hg
Question 46 Explanation: 
For diagram A, Pt = 76 cm Hg For diagram B, Pm + Patm = Pt = 76 + 10 = 86
Question 47
The diagram below shows a U-tube containing water and oil. Given that the density of water is 1000 kg m-3, what is the density of oil (in g cm-3) ? 47
A
0.80
B
1.25
C
0.90
D
1.11
Question 47 Explanation: 
hw X pw X g = ho X po X g 8 x 1 x g = 10 x po x g po = 0.8 g cm^-3
Question 48
Some air is trapped in a mercury barometer as shown in the diagram. If the atmospheric pressure is 75 cm Hg, what is the pressure exerted by the trapped air? 48
A
30 cm Hg
B
60 cm Hg
C
15 cm Hg
D
45 cm Hg
Question 48 Explanation: 
Pm + Pt = Patm Pt = 75 - 60 = 15 cm Hg
Question 49
Which of the diagrams shows the best design for the dam wall reservoir? 49
A
A
B
B
C
C
D
D
Question 49 Explanation: 
The pressure increases with depth, so wall thickness should also increase in thickness to manage the pressure.
Question 50
A long tube sealed at one end is filled with mercury and then placed vertically with its open end dipping below the surface of some mercury contained in a dish that is opened to the atmosphere. The tube is found to be full of mercury. Which of the following could explain this fact?
A
Air is introduced into the tube during transfer to the dish.
B
The capillary effect makes the mercury fill up the tube.
C
The tube is 600 mm long.
D
The tube is narrower at the bottom than at the top.
Question 50 Explanation: 
Pressure due ti a fluid is independent of cross-sectional area, it is proportional to the height of the fluid at the particular point.
Question 51
The diagrams below show the same thin tube containing air trapped by a mercury thread, held in four different positions, P, Q, R and S. (The diagrams are not drawn to scale.) In which order must the diagrams be placed (from left to right) to show that the volume of the trapped air is increasing? 51
A
P Q R S
B
S P Q R
C
R S P Q
D
Q R S P
Question 51 Explanation: 
The trapped air in Q will have the highest pressure, thus it will occupy the smallest volume. The pressure of the trapped air in P will be the smallest, thus it will occupy the biggest volume.
Question 52
A lady weighs 500 N and wears stiletto shoes. The area of the stiletto heel is 0.0001 m2. The pressure the lady exerts by standing on one stiletto heel is (in N m-2) 52
A
200
B
5000
C
500000
D
5000000
Question 52 Explanation: 
P = F / A = 500 / 0.0001 = 50,00,000 N/m^2
Question 53
Assume that the atmospheric pressure at sea level is equal to the pressure exerted by 0.76 m of mercury and the acceleration of free fall does not vary with height. If the average density of air is 1.2 kg m-3 and that of mercury is 13600 kg m-3, the atmospheric pressure at 3400 m above the sea level is equal to the pressure exerted by
A
1.060 m of mercury
B
0.460 m of mercury
C
0.760 m of mercury
D
0.300 m of mercury
Question 53 Explanation: 
Patm = hpg = 0.76 x 13600 x 10 = 103360 Pa Pressure due to 3400 m of air = hpg = 3400 x 1.2 x 10 = 40800 Pa Pressure at a height of 3400 m = 103360 - 40800 = 62560 Pa 62560 = h x pm x g h = 62560 / (13600 x 10) h = 0.46 m Hg
Question 54
A column of gas is slowly compressed as shown in the diagram. Which of the following graphs correctly shows the relation between the gas pressure P and the length of the gas column h? 54
A
A
B
B
C
C
D
D
Question 54 Explanation: 
Pressure is inversely proportional to volume. Thus, Pressure is inversely proportional to height (provided cross-sectional area is constant).
Question 55
The following diagrams show, to the same scale, the vertical cross-sections of each set of vessels. All of the vessels have circular horizontal cross-sections. They all contain water to the same level. Which one of the following statements about them is correct? 55
A
They each have the same pressure on the base.
B
The vertical-sided vessels have the greatest pressure on the base.
C
Vessel (iv) has the least pressure on its base.
D
Vessel (i) has the greatest pressure on its base.
Question 55 Explanation: 
The pressure experienced by the base is dependent on the height of the fluid.
Question 56
The apparatus shown is connected to a gas tap in order to measure the pressure of the gas. The tube P contains water and the tube Q contains some other liquid, the liquid levels in the tubes being originally at X. When the gas is turned on, the water in the open limb P rises to a higher level than that of the liquid in the open limb of Q as shown in the above diagram. This is because 56
A
the liquid in Q is denser than water.
B
tube P is closer to the gas inlet than tube Q.
C
there is more liquid in tube Q than in tube P.
D
the pressure of the gas exerted on P is higher than the pressure of the gas exerted on Q.
Question 56 Explanation: 
The density of the fluid used will affect the height attained.
Question 57
In an experiment to investigate the relationship between the volume V of a fixed mass of gas and the pressure P, a graph of PV against P is plotted. Which one of the following graphs shows the correct relationship at constant temperature? 57
A
A
B
B
C
C
D
D
Question 58
The diagrams (a) and (b) show an open-ended and a closed tube manometer connected (at different times) to the same gas cylinder. The mercury barometer reads 760 mm atmospheric pressure. Assume that there is no loss in the pressure from the gas cylinder. What is the height x of the mercury in the diagram (b)? 58
A
100 mm
B
660 mm
C
760 mm
D
860 mm
Question 58 Explanation: 
Pgas = 100 + 760 = 860 mm Hg
Question 59
The diagram shows a mercury barometer. The height h of the mercury column is recorded. The barometer is set up on another planet where the atmospheric pressure is half that of the Earth and the gravitational field strength is double of that on Earth. Which is the height recorded? 59
A
0.25h
B
0.5h
C
h
D
2h
Question 60
The pressure exerted by a water jet of area 5 mm2 is 20 MPa (20 000 000 Pa). What is the force exerted on the ground if the jet of water strikes the ground vertically? 60
A
100 N
B
1,00,000 N
C
10,00,000 N
D
10,00,00,000 N
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