2017 - JAMB Physics Past Questions and Answers - page 2
11
A block and tackle pulley arrangement has 6 pulleys in which an effort of 50N supports a load of 200N, calculate the efficiency of the machine
A
80.0%
B
76.6%
C
66.7%
D
60.7%
correct option: c
Efficiency = \(\frac{ma}{V.R}\) x \(\frac{100}{1}\)
V.R = number of pulleys = 6
ma = \(\frac{\text{Load}}{\text{Effort}}\) = \(\frac{200}{50}\) = 4
Effiecieny = \(\frac{4}{6}\) × 100 = 66.67%
Users' Answers & CommentsV.R = number of pulleys = 6
ma = \(\frac{\text{Load}}{\text{Effort}}\) = \(\frac{200}{50}\) = 4
Effiecieny = \(\frac{4}{6}\) × 100 = 66.67%
12
Three 3ω resistance are connected in parallel what is the equivalent resistance?
A
1ω
B
9ω
C
3ω
D
0.33ω
correct option: a
Resistor connected in a parallel have an equivalence given by
\(\frac{1}{\text{Reff}}\) = \(\frac{1}{3}\) + \(\frac{1}{3}\) + \(\frac{1}{3}\)
= \(\frac{1 + 1 + 1}{3}\) = \(\frac{3}{3}\) = 1
Reff = 1ω
Users' Answers & Comments\(\frac{1}{\text{Reff}}\) = \(\frac{1}{3}\) + \(\frac{1}{3}\) + \(\frac{1}{3}\)
= \(\frac{1 + 1 + 1}{3}\) = \(\frac{3}{3}\) = 1
Reff = 1ω
13
Which of the following instruments helps to maintain the correct humidity and temperature of a building?
A
A compressor
B
A refrigerator
C
Air blower
D
Air conditioner
correct option: d
Compressor is an instrument to supply air or other gas at increased pressure
Refrigerator is an appliance to keep things cold
Air blower is used to release air
Air conditioner is used to remove heat and maintain a stable temperature in an occupied space
Users' Answers & CommentsRefrigerator is an appliance to keep things cold
Air blower is used to release air
Air conditioner is used to remove heat and maintain a stable temperature in an occupied space
14
An element and its isotope only differ in the number of
A
protons
B
electrons
C
ions
D
neutrons
correct option: d
Isotopy is due to difference in mass number, what causes the difference is the difference in the number of neutrons present
Users' Answers & Comments15
The thermal expansion of a solid is an advantage in
A
Balance wheel of a watch
B
Construction of steel rail lines
C
Construction of large steel bridges
D
Fitting of tyres on wheels
correct option: a
Thermal expansion of a solid is majorly advantageous in the use of bimetallic strip in the balance of a watch so as not to lose time
Users' Answers & Comments16
The S.I unit of moment of a force is
A
kgm
B
µm
C
Jm
D
µm\(^{-1}\)
correct option: b
Moment of a force is the product of a force and the perpendicular distance from the line of action of the force
Moment = force × distance
= N × m
= Nm
Users' Answers & CommentsMoment = force × distance
= N × m
= Nm
17
A block and tackle pulley arrangement has 6 pulleys in which an effort of 50N supports a load of 200N, calculate the efficiency of the machine
A
80.0%
B
76.6%
C
66.7%
D
60.7%
correct option: c
Users' Answers & Comments18
Calculate the light of the image formed by a pinhole camera of length 12cm used to photograph an object 60cm away from the hole and 70cm high
A
10 cm
B
16 cm
C
5 cm
D
14 cm
correct option: d
Magnification = \(\frac{\text{Length of camera}}{\text{distance of object from pin hole}}\)
m = \(\frac{12}{60}\)
= 0.2
Also magnification m = \(\frac{\text{Height of image}}{\text{Height of object}}\)
∴ Height of image = m × height of object
= 0.2 × 70
= 14cm
Users' Answers & Commentsm = \(\frac{12}{60}\)
= 0.2
Also magnification m = \(\frac{\text{Height of image}}{\text{Height of object}}\)
∴ Height of image = m × height of object
= 0.2 × 70
= 14cm
19
When two objects P and Q are supplied with the same quantity of heat, the temperature change in P is observed to be twice that of Q. The mass of P is half that of Q. The ratio of the specific heat capacity pf P to Q is
A
1:4
B
4:1
C
1:1
D
2:1
correct option: c
H = mcθ
HP = HQ, θP = 2θ,
mP = \(\frac{1}{2}\)mQ
∴ HP = mQCPθP, also HQ = mQCQθQ
Since HP = HQ
∴ mPcPθP = mQcPθq
Putting in the conditions
\(\frac{1}{2}\)mQ × cP × 2θQ = mQ × θQ × cQ
∴ cP = cQ
\(\frac{C_p}{C_Q}\)= \(\frac{1}{1}\)
= 1:1
Users' Answers & CommentsHP = HQ, θP = 2θ,
mP = \(\frac{1}{2}\)mQ
∴ HP = mQCPθP, also HQ = mQCQθQ
Since HP = HQ
∴ mPcPθP = mQcPθq
Putting in the conditions
\(\frac{1}{2}\)mQ × cP × 2θQ = mQ × θQ × cQ
∴ cP = cQ
\(\frac{C_p}{C_Q}\)= \(\frac{1}{1}\)
= 1:1
20
When the r.m.s value of a source of electricity supply is given as 240v, it means that the peak value of the supply is
A
240v
B
340v
C
480v
D
57600v
correct option: b
The relationship between the peak value and r.m.s value of electricity supply is given as
V\(_{r.m.s}\) = \(\frac{V_o}{\sqrt{2}}\)
where Vo = peak voltage
∴ Vo = V\(_{r.m.s}\) × √2
= 240 × √2
= 339.5v
= 340v
Users' Answers & CommentsV\(_{r.m.s}\) = \(\frac{V_o}{\sqrt{2}}\)
where Vo = peak voltage
∴ Vo = V\(_{r.m.s}\) × √2
= 240 × √2
= 339.5v
= 340v