2011 - JAMB Physics Past Questions and Answers - page 2
11
A machine is used to lift a load of 20 N through a height of 10 m. if the efficiency of the machine is 40%, how much work is done?
A
80 J
B
500 J
C
300 J
D
120 J
correct option: b
Efficiency = \( \frac{\text{work output}}{\text{work input}} \times \frac{100}{1} \)
= 40 = \( \frac{20 \times 10 }{x} \times \frac{100}{1} \)
= 500J
Users' Answers & Comments= 40 = \( \frac{20 \times 10 }{x} \times \frac{100}{1} \)
= 500J
12
I. Density of the liquid.
II. Depth below the surface of the liquid.
III. Surface area of the liquid.
In which of the statement above will pressure be dependent?
II. Depth below the surface of the liquid.
III. Surface area of the liquid.
In which of the statement above will pressure be dependent?
A
I and II only.
B
II and III only.
C
I, II and III only.
D
I and III only.
correct option: a
Pressure in liquid is independent of cross sectional area of the container/ liquid
∴ the correct options are I & II
Users' Answers & Comments∴ the correct options are I & II
13
Which of the following could be effectively used to reduce friction?
A
kerosene
B
grease
C
water
D
petrol
14
Which of the following types of waves needs a medium for propagation?
A
sound waves
B
light waves
C
radio waves
D
x - rays
correct option: a
Sound is the only mechanical wave among the rest which are electromagnetic waves.
Users' Answers & Comments15
Which of the following electromagnetic waves has the highest frequency?
A
utra - violet rays
B
radio waves
C
x - rays
D
infrared - rays
correct option: c
r - rays has the highest frequency followed by X - rays, ultraviolet ray, visible light intra - red and the least is radio weaves
Users' Answers & Comments16
A perfect emitter or absorber of radiant energy is a
A
conductor
B
black body
C
white body
D
red body
correct option: b
Dull, black surface are good emitters or absorbers of energy
Users' Answers & Comments17
The ground is always cold at night because the
A
atmosphere absorbs the sun's energy at night
B
earth radiates heat to the atmosphere at night
C
sun no longer shine at night
D
atmosphere reflects the sun's energy at night
correct option: b
The earth radiate heat to the atmosphere at night thereby lowering the temperature of the ground
Users' Answers & Comments18
A cannon is fired from town X,after how long is the sound heard at a town Y 4.95 km away?
[velocity of sound in the air = 330 ms-1]
[velocity of sound in the air = 330 ms-1]
A
30 s
B
10 s
C
10 s
D
15 s
correct option: a
V = (2X)/t
330 = (2 x 4.95 x 103)/t
t = (9.9. x 103/330 = (9900)/330 = (90)/3
= 30 secs
Users' Answers & Comments330 = (2 x 4.95 x 103)/t
t = (9.9. x 103/330 = (9900)/330 = (90)/3
= 30 secs
19
The phenomenon that shows that increase in pressure lowers the melting point can be observed in
A
sublimation
B
condensation
C
coagulation
D
regelation
correct option: d
Regelation means refreezing a phenomenon whereby melted ice free from increased pressure refreezed when they are released from the pressure.
Users' Answers & Comments20
A block of aluminum is heated electrically by a 30 w heater if the temperature rises by 10°c in 5 minutes, the heat capacity of the aluminum is
A
900 JK-1
B
90 JK-1
C
100 JK-1
D
200 JK-1
correct option: a
Heat supplied = Heat gained Pt = MCDθ
30 x 5 x 60 = c x 10
where c = mc which is the heat capacity
c = (30 x 5 x60)/10 = 900 JKg-1
Users' Answers & Comments30 x 5 x 60 = c x 10
where c = mc which is the heat capacity
c = (30 x 5 x60)/10 = 900 JKg-1