Problem Set 3
(10 points) Exercise 11.35 on page 370 (Ch. 11) of the textbook.
(12 points) Exercise 11.53 on page 379 (Ch. 11) of the textbook.
(10 points) Exercise 12.25 on page 397 (Ch. 12) of the t
(iii) From time t= Os to 2‘: 50s, the recorded count rate varies from 88 SUQgested SOIUtiOhS to
to 91, this variation is due to the random nature of the radioactive ‘ si cs
From time I: 605 to t= 70s, the recorded count rate decreases
—- " 2— n=4 No. ofhalf-life is 4.
(2) 16 ( )
So half-life = 1 hour 2 W =15 minutes
The use of screwjack cannot improve the efficiency because
energy is lost in overcoming friction and raising the movable
output - input
The output energy of a machine is always equal to or less
than the input energy because the efficiency of the machine is
100% or less.
The advantage of using machine is that we can use a smaller
effort to lift/raise
For the lst statement,
P = Y— :> R = V—
. , . 2002
Resustance ofa ‘200V, 100W light bulb : 100 = 400 Q
. , . 2002
Resxstance of a ‘200V, 40W light bulb = 40 = 1000 Q
With V being constant, the higher the rated power o
99 Suggested Solutions to
Average Speed = Total distance travelled
Total time taken
_ 120 + 100
_ 30 + 20
= 4. 4 ms‘1
Statements (2) is correct because both spheres have an acceleration of 10 ms'z.
Statement (1) is correct because both
For 1st statement,
W and R are not an action and reaction pair because they are
acting on the same body, the object.
For 2nd statement,
W and R are equal in size (magnitude) and opposite in
direction. So the statement is true.
But they do not
1990—PHY II M
Energy (latent heat of vaporization) is absorbed by water i
when it is boiling to overcome the bondings between
molecules before changing into gas. So the lst statement is
Temperature is a measure of average kinetic energy. When
l991-PHY II 1992 P
0 Half-life of a substance is the time taken for its activity to ﬂ
drop to half of its initial value.
Initial activity = 40 disintegrations per minute
So half-life is the time taken for the activity to drop to 20
disintegrations per min
(1) Work = Force X displacement in the direction of
Unit = Nm = J
Unit of Potential energy is alsojoule (J)
(2) Moment (Torque) = force >< perpendicular distant
Unit = Nm
Momentum 2 mass >< velocity
2014 INTERIM REPORT
Highlights of 2014 interim results
Group operating earnings amounted to
HK$4,768 million, a 22.4% increase over the
corresponding period in 2013
Total earnings including net gain on CAPCO
and PSDC acquisitions increased 78.4% to
Moody's Investors Service Hong Kong
Moodys Investors Service Hong Kong
: (no. 388419) 6/11/2015
Moodys Investors Service Hong Kong Ltd.
Range Study Centre - - Education Services
The Hong Kong and China
Gas Company Limited
(Stock Code: 3)
De veloping E nv ironmentallyfriendly Ne w Energy
Advancing our expertise to remain at the
forefront of the new energy sector
A Leader in
Mainl and Ut ili t ies
In perfectly elastic collision, mechanical energy is conserved.
i.e. the amount of kinetic energy before the collision is equal
to that after the collision. So options A and C are NOT
Energy cannot be created or destroyed. The
l990-PHY II l990-PHY II
' For statement (1 ),
1 Y is the speed.
, (increasing velocity
v2 : “2 +21” For statement (2),
u = 0 (initially at rest) ‘ s
v2 = 2as Y is the distance travelled.
Slope of v2 — s graph = 2a (sl