A copper cube weighs 0.25 N in air, 0.17N when completely immersed in paraffin oil and 0.15 N when completely immersed in water.The ratio of upthrust in oil to upthrust in water is
คำตอบ
(B)
4 : 5
2
A wheel and axle is used to raise a load of 500 N by the application of an effort of 250 N. If the radii of the wheel and the axle are 0.4 cm and 0.1 cm respectively, the efficiency of the machine is
คำตอบ
(C)
50 %
3
The hydrostatic blood pressure difference between the head and the feet of a boy standing straight is 1.65 x 104 Nm-2. Find the height of the boy.
[ Density of blood = 1.1 x 103 kgm-3, g = 10ms-2]
คำตอบ
(C)
1.5 m
4
A body weighing 80N stands in an elevator that is about to move. The force exerted by floor on the body as the elevator moves upward with an acceleration of 5 ms-2 is
[g = 10ms-2]
คำตอบ
(C)
120 N
5
If the distance between two suspended masses 10kg each is tripled, the gravitational force of attraction between them is reduced by
คำตอบ
(D)
one ninth
6
Two force each of 10N acts on a body, one towards the north and the other towards the east.
The magnitude and the direction of the resultant force are
คำตอบ
(D)
10√2N, 45°E
7
A particle in circular motion performs 30 oscillation in 6 seconds. Its angular velocity is
คำตอบ
(D)
10π rad s-1
8
The effect of a particle in a fluid attaining its terminal velocity is that the
คำตอบ
(B)
weight is equal to the retarding force
9
A coin place below a rectangular glass block of thickness 9cm and refractive index 1.5 is viewed vertically above the block. The apparent displacement of the coin is
คำตอบ
(A)
3 cm
10
The radiator of a motor car is cooled by
คำตอบ
(C)
convection
11
I. Temperature.
II. Density of air molecules
III. Pressure
IV. Pitch
Which of the above will affect the velocity of sound in the air
คำตอบ
(A)
I and II only
12
Which of the following is a characteristics of stationary waves?
คำตอบ
(A)
They are formed by two identical waves travelling in opposite directions
13
To produce an enlarged and erect image with a concave mirror,the object must be positioned
คำตอบ
(D)
between the principal focus and the pole
14
the property that is propagated in a traveling wave is
คำตอบ
(C)
energy
15
Which of the following eye defects can be corrected using a cylindrical lens.
คำตอบ
(B)
Astigmatism
16
The time rate of loss of heat by a body is proportional to the
คำตอบ
(A)
difference in temprature between the body and its surroundings
17
If tension is maintained on a stretched string of length 0.6m, such that its fundamental frequency of 220Hz is excited, determine the velocity of the transverse wave in the string.
คำตอบ
(B)
264 ms-1
18
A concave mirror of radius of curvature 40 cm forms a real image twice as large as the object.
the object distance is
คำตอบ
(B)
30 cm
19
water is a poor thermometric liquid because it
คำตอบ
(C)
wets glass
20
a ray of light which strikes a glass slab from air at normal incidence passes through the slab
คำตอบ
(A)
undeviated and undisplaced at a lower speed
21
blowing air over a liquid aids evaporation by
คำตอบ
(B)
decreasing its vapour pressure
22
The phenomenon that makes sound persist when its source has been removed is known as
คำตอบ
(D)
reverberation
23
the pressure of 3 moles of an ideal gas at a temperature of 27°C having a volume of 10-3m3 is
คำตอบ
(D)
7.47 x 106-2
24
Vibration in a stretched spring cannot be polarized because they are
คำตอบ
(C)
longitudinal waves
25
The diagram above show s the force-extension curve of a piece of wire. The energy stored when the wire is stretched from E to F is?
คำตอบ
(D)
7.5 x 10-1J
26
The diagram above shows the force (F) acting on an object through a distance (x). The work done on this object is expressed as
คำตอบ
(B)
Fx/2 J
27
Calculate the refractive index of the material for the glass prism in the diagram above
คำตอบ
(C)
√2
28
From the diagram above, determine the value of the resistance X
คำตอบ
(D)
15Ω
29
The energy stored in a capacitor of capacitance 10μF carrying a charge of 100μC
คำตอบ
(D)
5 x 10-4 J
30
When connected to a mains of 250V, the fuse rating in the plug of an electric device of 1 KW is
คำตอบ
(C)
4 A
31
The eye controls the amount of light reaching the retina by adjusting the
คำตอบ
(B)
iris
32
An electric iron is rated 1000W, 230V. What is the resistance of its elements?
คำตอบ
(B)
52.9Ω
33
The electric field between two - point charges is shown in the diagram above. What types of charges are at X and Y?
คำตอบ
(B)
Both X and Y are positive
34
The electromagnetic wave that can produce a heating effect on the environment is
คำตอบ
(C)
infrared rays
35
an electric cell with nominal voltage E has a resistance of 3Ω connected across it. If the voltage falls to 0.6E, the internal resistance of the cell is
คำตอบ
(B)
2Ω
36
\(^{23}_{11}\)Na + X → \(^{20}_9\)F + \(^4_2\)He
What particle is X in the reaction above?
คำตอบ
(C)
Neurons
37
Pure silicon can be converted to a p-type by adding a controlled amount of
คำตอบ
(A)
trivalent atoms
38
The energy associated with the photon of a radio transmission at 3 x 105 Hz is
[h = 6.63 x 10-34Js]
คำตอบ
(A)
2.00 x 10-28J
39
The percentage of the original nuclei of the sample of a radioactive substance left after 5 half - lives is
คำตอบ
(C)
3%
40
From the generating station to each substation power is transmitted at a very high voltage so as to reduce
คำตอบ
(D)
heating in the coils
41
The particle that is responsible for the nuclear fission in a nuclear reactor is
คำตอบ
(A)
neutron
42
A transistor is used in the amplification of signals because it
คำตอบ
(A)
controls the flow of current
43
The carbon-granules microphone works on the principle of change in
คำตอบ
(B)
resistance
44
At what frequency would a capacitor of 2.5μF used in the radio circuit have a reactance of 250Ω
คำตอบ
(B)
\(\frac{800}{\pi}\) Hz
45
A current of 0.5 A flowing 3h Deposits 2g of metal during electrolysis. The quantity of the same metal that would be deposited by the currents of 1.5A flowing in 1h is
