ENGINEERING SCIENCE

15) A bottle containing 1.5 kg of water at 340C is put into a refrigerator. What is
the temperature of the water after 1.575 x 105 J of heat has been removed
from the water ? ( Cwater = 4200 J kg-1 OC-1 )

Answer : Tf = 90C

16) 3 kg of gold at a temperature of 20 0C is placed into contact with 1 kg of
copper at a temperature of 80 0C. Then the two substances reach thermal
equilibrium at 50ºC. (Given : the specific heat of gold is 130 J/kg ºC)
a) What is heat gained by the gold ?
b) What is the specific heat capacity of the copper?

Answer : a) Q = 11 700 J b) c = 390 J/ kg ºC

Chapter 6- Temperature and Heat/ Page 244

17) A metal sphere of 100 oC is placed in a beaker containing 0.2 kg of water at
20oC. If the final equilibrium temperature is 30 oC and no heat is lost to the
beaker, find:
a) The heat absorbed by the water
b) The mass of metal sphere
Specific heat capacity of metal sphere = 460 J kg-1 oC-1
Specific heat capacity of water = 4200 J kg-1 oC-1

Answer : a) Q = 8 400 J b) m = 0.26 kg

18) A 150 g quantity of certain metal, initially at 120 oC, is dropped into an insulated
beaker containing 100 g of water at 20 oC. The final temperature of the metal and
water in the beaker is measured as 35 oC. Assume that the heat capacity of the
beaker can be ignored. (C water = 4200 J kg-1 oC-1)
a) How much heat has been transferred from the metal to the water?
b) What is the specific heat capacity of the metal?

Chapter 6- Temperature and Heat/ Page 245

Answer : a) Q = 6 300 J b) c = 494.12 J kg-1 OC-1

19) A mechanic dropped a steel nut of mass 0.02 kg and temperature of 90 oC into
0.25 kg of water at 24 oC in a polystyrene cup. What is the temperature when the
steel nut and water have come to thermal equilibrium?
( C water = 4200 J kg-1 0C-1 and C steel = 450 J kg-1 oC-1 )

Answer : Tf = 24.56 oC

Chapter 6- Temperature and Heat/ Page 246

20) A 100 g brass block at 90oC is placed in a plastic foam cup containing 200 g of water at
20oC. No heat is lost to the cup or surrounding. What is the final temperature of the
mixture? Cwater = 4200 J kg-1 oC-1 , Cbrass = 380 J kg-1 oC-1

Answer : Tf = 23.03 0C

21) The steel ball bearing of mass 0.02 kg and the temperature 95 0C is placed into
0.2 kg of water at 24 0C in a polystyrene cup. What is the temperature when the
ball bearing and water have come to thermal equilibrium? Assume that the
exchange of heat is between the ball bearing and water only.
( Specific heat capacity of water = 4.2 x 103 J kg-1 OC-1 )
( Specific heat capacity of steel = 0.45 x 103 J kg-1 OC-1 )

Answer : Tf = 24.750C

Chapter 6- Temperature and Heat/ Page 247

22) The figure shows a metal ball about to be lowered into a plastic glass of water. What
is the equilibrium temperature of the ball and water?

m = 200 g
c = 480 J kg-1 0C-1
Initial temperature = 200C
m = 800 g
c = 4200 J kg-1 0C-1
Initial temperature = 800C

Answer : Tf = 78.330C

23) A 2 kg block of copper at 100 0C is placed into 1 kg of water in a 2 kg iron pot. The
water and the iron pot are at 25 0C just before the copper block is placed into the pot.
What is the final temperature of the water, assuming negligible heat flow to the
environment ?
( Ccopper = 0.4 kJ kg-1 0C-1 , Ciron = 0.5 kJ kg-1 0C-1 , Cwater = 4.2 kJ kg-1 0C-1 )

Chapter 6- Temperature and Heat/ Page 248

Answer : Tf = 350C

24) A 10 g of metal cube has been heating to a 1000C and is transferred into 12 g of water
at 140C in calorimeter copper. The calorimeter is weight 5 g while a specific heat
capacity for a copper and water of 400 Jkg-1 0C-1 and 4200 J kg-1 0C-1 respectively. If a
temperature of water and calorimeter upgrade to 210C, find the value of specific heat
capacity of the metal.

Answer : c = 464.3 J/kg 0C

Chapter 6- Temperature and Heat/ Page 249

25) The cooling system of a car engine contains 20 L of water. ( *1 L @ 1000 cm3 of water
has a mass of 1 kg)

a) What is the change in temperature of the water if the engine operates until 836 kJ
of heat are added?

b) Suppose it is winter, and the system is filled with methanol. The density of
methanol is 0.8 g/cm3. What would be the increase in the temperature of the
methanol if it absorbed 836 kJ of heat ?

c) Which is the better coolant, water or methanol? Explain.
(Given : Cwater = 4.18 kJ kg-1 0C-1 , Cmethanol = 2.45 kJ kg-1 0C-1 )

Answer : a) =10 0C b) = 21.3 0C

Chapter 6- Temperature and Heat/ Page 250

26) A plastic bag containing 0.80 kg of soup at 38oC is put into the freezer
compartment of a refrigerator. Calculate the amount of heat that must be removed
to completely solidify the soup. Assume the soup solidify at -2oC.
(Specific heat capacity of the soup, c = 4250 J/kg0C,
Specific latent heat of fusion of the soup, L = 3.38 x 105 J kg-1)

Answer : Q = 4.06 x 105 J or 406 400 J

27) A small pot contains 2.0 kg of water at 25 oC. Q1 of heat energy was supplied to the
water to increase its temperature to its boiling point of 100 oC and Q2 of heat energy
was required to boil away all the water into steam at the same temperature. Calculate
the values of Q1 and Q2
(Specific heat capacity of water, c = 4200 J/kg oC, Specific latent heat of vaporization
of water, l = 2.26 x 106 J kg-1)

Answer : Q1 = 6.3 x 105 J or 630 000 J, Q2 = 4.52 x 106 J or 4 520 000 J

Chapter 6- Temperature and Heat/ Page 251

28) Calculate the total amount of heat that must be removed to convert 0.40 kg of water at
30oC to ice at -5oC.
(Specific heat capacity of water is 4200 J/kg0C, Specific heat capacity of ice is 2000
J/kg0C, Specific latent heat of fusion of ice = 3.36 x 105 J kg-1)

Answer : Q = 1.89 x 105 J or 188 800 J

Chapter 6- Temperature and Heat/ Page 252

CONCEPT MAP

Chapter 6- Temperature and Heat/ Page 253

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ENGINEERING SCIENCE (DBS 10012) is specially written for
diploma students taking engineering science course at
Polytechnic Malaysia. It contain all the topics stipulated in
the revised Engineering Science DBS10012 syllabus for first
semester.

All physics concepts are presented clearly in simple way
for easy understanding. Worked examples are provided
for every subtopic to show how physics problems are
solved. Practice exercise placed at the end of the
subtopics provided immediate practice to enforce the
preceding concepts and skills. Tutorial at the end of each
chapter provide a very wide range of exam-type
questions. In total, more than 200 questions are provided
so that so that students can adequately prepare for their
examinations.

It is hoped that this book will help diploma students master
the basic concept of physics as well as prepare them to
pursuing engineering course.

Hafiza binti Ibrahim
Siti Noor binti Othman
Azia Idayu binti Awang