1997 - JAMB Physics Past Questions and Answers - page 2
11
A load of 20N on a wire of cross-sectional area 8 x 10-7m2, produces an extension of 10m2. calculate Young's modulus for the material of the wire if its length is 3m
A
7.0 x 1011Nm-2
B
7.5 x 1011Nm-2
C
8.5 x 1011Nm-2
D
9.0 x 1011Nm-2
correct option: b
Young's modulus = \(\frac{F}{A}\) \(\div\) \(\frac{e}{L}\)
= \(\frac{20}{8 \times 10^{-7}}\) \(\div\) \(\frac{10^{-4}}{3}\)
= 7.5 x 1011Nm-2
Users' Answers & Comments= \(\frac{20}{8 \times 10^{-7}}\) \(\div\) \(\frac{10^{-4}}{3}\)
= 7.5 x 1011Nm-2
12
A cube of sides 0.1m hangs freely from a string. What is the upthrust on the cube when totally immersed in water? [density of water is 1000kgm-2, g = 10ms-2]
A
1000 N
B
700 N
C
110 N
D
10 N
correct option: d
Volume of water displaced = volume of cube
therefore, 0.1 x 0.1 x 0.1 = 0.001m3
mass of H2O = 0.001 X 1000
= 1kg
upthrust = mg
= 1 x 10
=10N
Users' Answers & Commentstherefore, 0.1 x 0.1 x 0.1 = 0.001m3
mass of H2O = 0.001 X 1000
= 1kg
upthrust = mg
= 1 x 10
=10N
13
A piece of wire gauze can be made to lie on water because
A
the wire guaze is less dense than water
B
the water molecules repels the wire guaze upwards
C
the water surface has the effect of an elastic thin skin
D
of the cohensive forces between the water and the wire guaze molecules
correct option: c
Users' Answers & Comments14
A liquid of mass 1.0 x 103kg fills a rectangular tank of length 2.5m and width 2.0m. If the tank is 4m high, what is the pressure at the middle of the tank?[g = 10ms-2]
A
1.0 x 104Nm-2
B
2.0 x 103Nm-2
C
1.5 x 103Nm-2
D
1.0 x 103Nm-2
correct option: d
Density of liquid = \(\frac{1 {\times} 10^3}{2.5 {\times} 2 {\times} 4}\)
= 50kgm3
pressure heg = 50 x 10 x \(\frac{4}{2}\)
= 1 x 103Nm-2
Users' Answers & Comments= 50kgm3
pressure heg = 50 x 10 x \(\frac{4}{2}\)
= 1 x 103Nm-2
15
An empty 60 litre petrol tank has a mass of 10kg. Its mass when full of fuel of relative density 0.72 is
A
7.2kg
B
33.2kg
C
43.2kg
D
53.2kg
correct option: c
R.d = \(\frac{\text {density of petrol}}{\text{density of water}}\)
0.72 = \(\frac{\text{density of petrol}}{1000}\)
Density of petrol =720kgm3
mass of petrol = 720 x 60 x 10-3
=43.2kg
Users' Answers & Comments0.72 = \(\frac{\text{density of petrol}}{1000}\)
Density of petrol =720kgm3
mass of petrol = 720 x 60 x 10-3
=43.2kg
16
The length of mercury thread when it is at 0oC, 100oC and at an unknown temperature \(\theta\) is 25mm, 225mm and 175mm respectively. The value of \(\theta\) is
A
85.0oC
B
80.0oC
C
75.0oC
D
70.0oC
correct option: c
\(\frac{\theta\ - 0}{100 - 0}\) = \(\frac{175 - 25}{225-25}\)
\(\theta\) = 75.0oC
Users' Answers & Comments\(\theta\) = 75.0oC
17
Equal masses of copper and rubber are raised to the same temperature. After sometimes, the copper was observed to be at a lower temperature because
A
the specific heat capacity of copper is lower than that of rubber
B
copper expands more than rubber
C
the specific heat capacity of rubber is lower than that of copper
D
rubber expands more than copper
correct option: a
Users' Answers & Comments18
Before starting a journey, the tyre pressure of a car was 3 x 105Nm-2 at 27oC. At the end of the journey, the pressure rose to 4 x 105Nm-2. Calculate the temperature of the tyre after the journey, assuming the volume is constant
A
400oC
B
300oC
C
273oC
D
127oC
correct option: d
\(\frac{P_1}{T_1}\) = \(\frac{ P_2}{T_2}\)
\(\frac{3 \times\ 10^6}{27 + 273}\) = \(\frac{4 \times\ 10^6}{0 + 273}\)
\(\theta\) = 127oC
Users' Answers & Comments\(\frac{3 \times\ 10^6}{27 + 273}\) = \(\frac{4 \times\ 10^6}{0 + 273}\)
\(\theta\) = 127oC
19
What happens when a, certain quantity of pure ice is completely changed to water at 0oC?
A
latent heat is absorbed, the mass remains constant, and the volume decreases
B
latent heat is given out, the mass remains constant and the volume decreases
C
latent heat is given out, the mass increases and the volume remains constant
D
latent heat is absorbed, the mass decreases and the volume increases
correct option: b
Users' Answers & Comments20
A heating coil rated at 100W is used to boil off 0.5kg of boiling water. The time taken to boil off the water is [specific latent heat of vaporization of water = 2.3 x 106Jkg-1]
A
1.15 x 109 s
B
1.15 x 107 s
C
1.15 x 105 s
D
1.15 x 104 s
correct option: d
Heat energy = Elect. energy
0.5 x 2.3 x 106 = 100t
t = 1.15 x 104s
Users' Answers & Comments0.5 x 2.3 x 106 = 100t
t = 1.15 x 104s