1994 - WAEC Physics Past Questions and Answers - page 4
31
A note of frequency of 2000Hz has a velocity of \(400ms^{-1}\). What is the wavelength of the note?
A
800m
B
200m
C
5m
D
2m
32
A cell of e.m.f. 1.5V and internal resistance of 2.5Ω is connected in series with an ammeter of resistance 0.5W and a resistor of resistance of 7.0Ω. Calculate the current in the circuit.
A
0.15A
B
0.20A
C
2.10A
D
3A
33
A ball is dropped from a height of 45m above the ground. Calculate the velocity of the ball just before it strikes the ground. (Neglect air resistance and take g as \(10ms^{-2}\)
A
21.2\(ms^{-1}\)
B
30\(ms^{-1}\)
C
300\(ms^{-1}\)
D
450\(ms^{-1}\)
correct option: b
\(v^2 = u^2+2as=0^2 + 2\times 10\times 45 \Rightarrow
v^2 = 900m^2s^{-2} \Rightarrow \
v = \sqrt{900m^2s^{-2}} \Rightarrow
v = 30ms^{-1}\)
Users' Answers & Commentsv^2 = 900m^2s^{-2} \Rightarrow \
v = \sqrt{900m^2s^{-2}} \Rightarrow
v = 30ms^{-1}\)
34
A body accelerates uniformly from rest at \(2ms^{-2}\). Calculate the velocity after traveling 9m
A
36\(ms^{-1}\)
B
18\(ms^{-1}\)
C
6\(ms^{-1}\)
D
4.5\(ms^{-1}\)
correct option: c
\(V^2= U^2+2as\) =\(0+ 2\times 2ms^{-2}\times 9 =36ms^{-1}\) thus
V=\(\sqrt{36m^2s^{-2}}\) = \(6ms^{-1}\)
Users' Answers & CommentsV=\(\sqrt{36m^2s^{-2}}\) = \(6ms^{-1}\)
35
A metal rod of length 40cm at 20°C is heated to a temperature of 45°C. If the new length of the rod is 40.05cm. Calculate its linear expansitivity
A
1.2 x \(10^{-5}K{-1}\)
B
2.5x \(10^{-5}K{-1}\)
C
3.5x \(10^{-5}K{-1}\)
D
4.5x \(10^{-5}K{-1}\)
correct option: e
\(\alpha = \frac{I_2-I_1}{I_1(\theta_2-\theta_1)} \ \Rightarrow \frac{40.05 - 40}{40 \times (45-20)} = 5.0 \times10^{-5}\)
Users' Answers & Comments36
500g of water is heated so that its temperature rises from 30°C to 72°C in 7 minutes. calculate the supplied per minute. (Specific heat capacity of water is 4200J\(kg^{-1}K^{-1}\)
A
9000J
B
12600J
C
21000J
D
25200J
correct option: b
\(\frac{Q}{t} = \frac{0.5\times4200\times(72-30)}{7}=12600J\)
Users' Answers & Comments37
An electric kettle rated 1500W boils away 0.3kg of a liquid at its boiling point every 300s. Calculate the specific latent heat of the vaporisation of the liquid
A
1.5 x \(10^6Jkg^-1\)
B
1.35 x \(10^6Jkg^-1\)
C
1.5 x \(10^5Jkg^-1\)
D
4.5 x \(10^2Jkg^-1\)
correct option: a
Pt=mI; I=\(\frac{1500\times300}{0.3}=1.5\times10^6Jkg^-1\)
Users' Answers & Comments38
\(500cm^{-3}\) of a gas is collected at 0°C and at a pressure of 72cm of mercury. What is the volume of the the gas at the same temperature and at a pressure of 76cm of the same mercury?
A
\(\frac{76\times500}{72}cm^3\)
B
\(\frac{72\times500}{76}cm^3\)
C
\(\frac{72\times76}{500}cm^3\)
D
\(\frac{76}{72\times500}cm^3\)
39
The pressure of air in a tire is \(22.5Nm^{-2}\) at 27°C. If the air in the tyre heats up to 47°C, calculate the new pressure of the air, assuming that no air leaks out and that the change in volume of the air can be neglected.
A
\(21.10Nm^{-2}\)
B
\(24Nm^{-2}\)
C
\(39.07Nm^{-2}\)
D
\(45Nm^{-2}\)
correct option: b
\(\frac{P_1}{T_1}=\frac{P_2}{T_2};P_2= \frac{22.5\times320K}{300K}=24Nm^{-2}\)
Users' Answers & Comments40
Calculate the time taken to heat 2kg of water from 50°C to 100°C in an electric kettle taking 5A, from a 210V supply. (Specific heat capacity of water = 4200\(kg^{-1}K{-1}\)
A
2.5 minutes
B
5.7 minutes
C
6.7 minutes
D
7.5 minutes
correct option: c
t = \(\frac{mc\theta}{p}= \frac{2\times4200\times50}{210\times5} \ = 400s = 6.7\)
Users' Answers & Comments