2008 - JAMB Physics Past Questions & Answers - page 5

41
THe diagram above shows a plank RS pivoted its center of gravity O and is in equilibrium with the weight P and Q. If a weight 2P is added to P the plank will be in equilibrium again by
A
moving Q nearer to O
B
moving P nearer to O
C
addding a weight Q to Q
D
moving P further away from O
CORRECT OPTION: b
If 2P is added P, the beam will bend at R side. So to keep it in equilibrium. P should be moved nearer to 0
42
The efficiency of the pulley system shown above is 80%. find the effort E required to lift the load of 1200N
A
275N
B
325N
C
375N
D
573N
CORRECT OPTION: c
VR = No. of pulleys = 4
Efficiency = M.A/V.R x 100% = load
Effort x 100%_V.R
∴80 = 1200 x 100 x 1100__Effort4
∴ Effort = 1200 x 100 = 375N_80 x 4
43
The diagram above is the heating curve for a solid QR is the
A
melting region
B
boiling region
C
sublimation region
D
evaporating process
CORRECT OPTION: a
At melting point there is no change temperature
44
The above figure shows the motion of a progressive wave along a string. The particle motion of the medium is in direction
A
parallel to OX
B
parallel to OY
C
60o to OX
D
60v to OY
CORRECT OPTION: b
Particles of the transmitting medium in transverse wave oscillate in a direction perpendicular to the propagation of the wave
45
If a convex lens of focal length 12cm is used to produce a real image four times the size of the object, how far from the lens must the object be placed?
A
10 cm
B
15 cm
C
20 cm
D
25 cm
CORRECT OPTION: b
Magnifications = V/U = 4
∴ V = 4U
1/V + 1/U = 1/f
1/4u + 1/U = 1/12
5/4U = 1/12
4U = 12 x 5 = 60
∴ U = 15 cm
46
Find the effective resistance in the diagram above
A
6 Ω
B
12 Ω
C
18 Ω
D
24 Ω
CORRECT OPTION: d
The resistors are in series
∴ Reff = R1 + R2 + .....
= 4 + 4 + 4 + 4 + 4 + 4 = 24 Ω
47
Given the inductor of inductance 5mH, 10mH and 20mH connected in series, the effective inductance is
A
0.35mH
B
3.50mH
C
2.90mH
D
35.0mH
CORRECT OPTION: d
Left = L1 + L2 + L3
= 5mH + 10mH + 20mH = 35mH
48
If electron are accelerated from rest through a potential difference of 10kv, what is the wavelength of the associated electron
[m = 9.1 x 10-31kg, e = 1.6 x 10-19C, h = 6.6 x 10-34js]
A
1.22 x 10-11m
B
3.87 x 10-10m
C
2.27 x 1011m
D
2.27 x 1014m
CORRECT OPTION: a
λ = __h
√(2evm)

= ____6.6 x 10-34
√(2 x 1.6x10-19 x 10000 x 9.1x10-34)

1.223 x 10-11m
49
14N + 4He → 17O + X
728

In the equation above, the particles X is
A
a proton
B
a neutron
C
an α - particle
D
a β - particle
CORRECT OPTION: a
for the conversion of mass 14 + 4 = 17 + x
∴ X = 18 - 17 = 1
for conservation pf charge:7 + 2 = 8 + y
y = 9 - 8 = 1
Thus, the element is 11X which is equal to hydrogen nucleus ( proton)
50
Find the median of 4, 1, 4, 1, 0, 4, 4, 2 and 0
A
o
B
1
C
2
D
4
CORRECT OPTION: c
0, 0, 1, 1, \(\bigcirc{2}\), 4, 4, 4, 4

median = 2
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