2021 - JAMB Physics Past Questions and Answers - page 2
A boy standing some distance from the foot of a tall cliff claps his hands and hears an echo 0.5s later. If the speed of sound is 340ms\(^{-1}\), how far is he from the cliff?
680m
170m
34m
85m
V = \(\frac{2d}{t}\)
v = 340ms\(^{-1}\)
t = 0.5s
d= ?
d = \(\frac{2d}{2} = \frac{340 \times 0.5}{2}\) = 85m
Which of the following is not a vector quantity?
momentum
force
temperature
displacement
Vector quantities are physical quantities characterized by the presence of both magnitude and direction. Examples of vector quantities are displacement, force, torque, momentum, acceleration, velocity, etc.
Scalar is a physical quantity that is completely described by its magnitude. Examples of scalars are speed, density, volume, energy, mass, time, etc.
Calculate the heat energy required to vaporize 50g of water initially at 80ºC if the specific heat capacity of water is 4.23jg\(^{-1}\)k\(^{-1}\) (specific latent heat of vaporization of water is 2260jg\(^{-1}\)
530000J
23200J
17200J
130000J
H = mc\(\bigtriangleup\theta\) + mL
m = 50g, c = 4.23J/gk,L = 2260, \(\bigtriangleup\theta\) = 80ºC
H = 50 [4.23 x 80 + 2260]
= 129920 \(\approx\) 130,000J
In a series R-L-C circuit at resonance, the voltages across the resistor and the inductors are 30V and 40V respectively. What is the voltage across the capacitor?
30V
40V
50V
70V
AT resonance; X\(_{L}\) = X\(_{c}\)
V\(_{L}\) = V\(_{c}\) = 40V
If the frequency of an emitted x-ray is 1.6 x 10\(^{16}\)Hz, the accelerating potential is?
[e = 1.6 x 10\(^{-19}\)J, h = 6.63 x 10-\(^{34}\)Js]
6630.0V
663.0V
66.3V
6.6V
Given:
f = 1.6 x10\(^{16}\)H\(_{3}\)
h = 6.63 x 10\(^{-39}\)Js
e = 1.6 x 10\(^{-19}\)C, V = ?
V = \(\frac{w}{e} = \frac{hf}{e}\)
= \(\frac{1.6 \times 10^{16} \times 6.63 \times 10^{34}}{1.6 \times 10^{-19}}\)
= 66.3V
If the fraction of the atoms of radioactive material left after 120 years is 1/64, what is the half-life of the material?
24 years
20 years
10 years
2 years
Given fraction of the atoms left = \(\frac{1}{64}\)
= \(\frac{1}{64} = \frac{1}{(2)^{6}}\)
\(\therefore\) = \(\frac{120 \text {years}}{6}\) = 20 years
\(\Rightarrow\) T\(\frac{1}{2}\)
= 20 years
A certain radioactive source emits radiation that was found to be deflected by both magnetic and electric fields. The radiation is?
beta rays
gamma rays
x-rays
ultra-violet rays
Because Alpha is positively charged and Beta is negatively charged, they are deflected in an electric or magnetic field, whereas Gamma radiations are not charged and as a result do not deflect in an electric or magnetic field.
The inner diameter of a test tube can be measured accurately using a?
micrometer screw gauge
pair of dividers
meter rule
pair of vernier calipers
Vernier callipers are used to measure the internal and external diameters of a tube
Two bodies have masses in the ratio3:1. They experience forces which impart to them, acceleration in the ratio 2:9 respectively. Find the ratio of forces the masses experienced
1:4
2:1
2:3
2:5
Given: \(\frac{m_{1}}{m_{2}} = \frac{3}{1}\) \(\Rightarrow\) m\(_{1}\) = 3m\(_{2}\)
\(\frac{a_{1}}{a_{2}} = \frac{2}{9}\) = a\(_{1}\) = \(\frac{2a_{2}}{9}\)
\(\frac{F_{1}}{F_{2}}\) = ?
F = ma
\(\Rightarrow\) \(\frac{F_{1}}{F_{2}} = \frac{m_{1}a_{1}}{m_{2}a_{2}}\)
= \(\frac{(3 \not m_{2})(2 \not a_{2})}{\not m_{2} a_{2} \not a_{3}}\)
\(\frac{F_{1}}{F_{2}} = \frac{2}{3}\) \(\Rightarrow\) 2:3
Particles of mass 10\(^{-2}\)kg is fixed to the tip of a fan blade which rotates with angular velocity of 100rad\(^{-1}\). If the radius of the blade is 0.2m, the centripetal force is?
2N
20N
200N
400N
Given:
m = 10\(^{-2}\)
w = 100rads\(^{-1}\)
F = mw\(^{2}\)r
r = 0.2m
= 10\(^{-2}\) x (100)\(^{2}\) x 0.2
= 20N