Worksheet for unit -2-
Physics Dept.
Grade 11A
Name:……………………………………………...
1- Work (W)
Work (W): is the amount of energy transferred by a force (F) acting through a displacement (d).
Or it is the product of applied force and travelled distance.
Work done = Force
W
. distance moved
= F
.
d
N
.
m
= N.m = Joule(J)
Problems
1. Deduce the unit of the work.
2. In the following figure:
If this object moves 20 m, calculate the work done on it.
3. In this figure:
If the work done is 500 J, find the distance travelled by this object.
4. In the following figure:
If this pram ‫ عربة أطفال‬moves 30 m, find the force applied on it.
5. Solve example 6.2 page 82 (physics course for “0” level).
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Physics Dept.
Worksheet for unit -2-
Grade 11A
Name:……………………………………………...
Continue
Work (W)
Problems
1. In this figure :
Calculate work.
2. A block is pushed horizontally ‫ أفقيا‬by a force of 10 N through a distance of 20 m. calculate the work
done.
3. In this figure:
Calculate the weight in (N)
4. Solve example page 97 (New physics for you).
5. Solve example page 110 (New physics for you).
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Physics Dept.
Worksheet for unit -2-
Grade 11A
Name:……………………………………………...
2- Kinetic and Potential Energy
A- Kinetic Energy: ‫الطاقة الحركية‬
It is the extra energy which it possesses due to its motion.
)‫هي الطاقة التي يمتلكها الجسم بسبب حركته (سرعته‬
Ek = (1⁄2) mv2 Joule (J)
Ek: Kinetic Energy , m: Mass
,
v: velocity
Problems
1. In this figure:
Calculate the kinetic energy.
2. In this figure:
Calculate the velocity of the elephant.
3. In this figure:
Calculate kinetic energy
4. Car moving with speed of 40 m/s, if its kinetic energy was 12x105 J, Find its mass.
5. What will happen to kinetic energy if the velocity is doubled?
6. Solve ex 3 page 109 (New physics for you)
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Physics Dept.
Worksheet for unit -2-
Grade 11A
Name:……………………………………………...
B- Potential Energy: ‫طاقة الوضع‬
It is the extra energy which it possesses due to its position.
)‫هي الطاقة التي يمتلكها الجسم بسبب موضعه (بعده عن سطح األرض‬
Ep = w.h
mg = w
‫قانون طاقة الوضع‬
Ep = mgh
Ep: potential Energy, m: Mass , h: hieght , g: gravitational acceleration= 10 m/s 2 w: weight
Problems
1. What P.E. is gained ‫تكتسب‬when a 100 kg object is raised 4.00 m straight up?
2. In this figure:
Calculate the potential energy.
3. An object weighing 10 N is lifted from the ground to a height of 3 m. Find its PE in the new
position.
4. Solve problem 4 page 112 (New physics for you)
Home work:
Which of these balls have higher potential energy? Why?
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Physics Dept.
Worksheet for unit -2-
Grade 11A
Name:……………………………………………...
3- Conservation of Energy
The low of conservation
“The energy can’t be created or destroyed but it is converted
from one form to another”
" ‫"الطاقة ال تفنى و ال تستحدث و لكنها تتحول من صورة ألخرى‬
Em = Ek + Ep
Where:
Em= total mechanical energy , Ek = kinetic energy , Ep = potential energy
(Ek + Ep)I = (Ek + Ep )f
Ep = Ek,
m×g×h = ½ mv2
v2 = 2gh
V=
2 gh
Problems
1. A 0.5 kg ball has a height of 5 meters and it is traveling 1 m/s. What is the ball’s mechanical energy?
2. If the kinetic energy of a falling object is 12 J and its potential energy is 35 J, what is its mechanical
energy?
3. A student drops an object of mass 10 kg from a height of 5 m. What is the velocity of the object
when it hits the ground? Assume, for the purpose of this question, that g = 10 m/s2
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Physics Dept.
Worksheet for unit -2-
Grade 11A
Name:……………………………………………...
4. A ball is dropped from a cliff ‫ منحدر‬of 100 meters
a) When will the ball have the highest gravitational potential energy?
b) When will the ball have the highest kinetic energy?
c) At about what point in the fall will the kinetic energy of the ball equal to the gravitational potential
energy?
d) Does the Mechanical Energy of the ball change during the drop? Why?
5. A 50 kg diver hits the water below (at a zero height) with a kinetic energy of 5000 Joules. The height
from which the diver dove was ____ meters
6. At what height above the ground must a mass of 10 kg be to have a potential energy equal in value
to the kinetic energy possessed by a mass of 10 kg moving with a velocity of 20 m/s?
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Worksheet for unit -2-
Physics Dept.
Grade 11A
Name:……………………………………………...
4- Power
Standard 11A.27.5
Define power as the rate of doing work or converting energy and solve problems using P = W/ t.
Power: it is the rate of doing work or converting energy.
P
=
W/ t
=
Fd/t
=
Watt
=
J /s
=
N.m /s
=
.‫معدل بذل شغل أو تحول الطاقة من صورة ألخرى‬
Fv
=
E/ t
N.m /s
=
J /s
Where P is power, W is work, E is energy, F is applied force, d is distance moved, v is velocity and t is
time.
Problems
1. If the work done on an object through 5 second was 20 J, find the power.
2. In this figure :
If time taken is 5 s, calculate the power
3. A force of 40 N is exerted on a mass, causing it to move with a constant speed of 5 m/s. What power
is used?
4. A girl weighing 500 N takes 50 s to climb a flight of stairs ‫ مصعد‬18 m high. Her power output
vertically is
5. A lift ‫ مصعد‬in a building raises ‫ يرفع‬a mass of 1500 kg through 30 m in 1 minute. What must be the
power of the motor?
6. A 95-kg student climbs 4.0 m up a rope in 3.0 seconds. What is the power output of the
student?
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Physics Dept.
Worksheet for unit -2-
Grade 11A
Name:……………………………………………...
5- Efficiency and Energy loss
Eefficiency: - is the ratio between the useful output energy and the input energy.
.‫ هي النسبة بين الطاقة الخارجة (المفيدة) إلى الطاقة الداخلة‬-:‫الكفاءة‬
Energy can be lost in form of waste heat.
.)‫الطاقة الميكانيكية يمكن أن تفقد على شكل حرارة (طاقة حرارية‬
Not all energy produced from any power supply can be used but there is some energy lost in other form of
energy such as waste heat you feel when you touch the car motor.
‫ليست كل الطاقة الناتجة من أى مصدر للطاقة يمكن االستفادة بها كاملة و لكن يوجد دائماا جا م مفقاود علاى صاورة حارارة ماى ب علاى سابيل‬
‫المىال عنادما تلمام محارل السايارة تباعر بحارارة و ذلا نتيجاة الطاقاة الميكانيكياة المفقاودة علاى صاورة طاقاة حرارياةب و كاكل فاي أسا ل‬
.‫الكهربام عندما تكون ساخنة فهكا يدل على أن الطاقة الكهربية تفقد على شكل حرارة‬
Efficiency = (useful output energy) / (total input energy) x 100 %
Eff = (Eoutput / Einput) x 100 %
Problems
1. Light lamp uses 20 J from 25 J source of energy; calculate the efficiency of this source.
2. Motor produces total energy of 2000 J but only 1500 J is the useful energy hat can be used, calculate
the efficiency of this motor.
3. Motor pump can raise 100 kg water for 10 m high; if the efficiency of this motor is 80 %, calculate
the total energy produced by this motor.
Assume g = 10m/s2.
4. Car with mass of 1500 kg can move at maximum velocity 150 m/s; if its motor efficiency is 90 %,
calculate the total energy produced by the motor.
5. Solve problem 6 page 67 (advanced physics for you).
6.
Home work A student of mass 65 kg climbs to the top of a building 30 m high. If the efficiency
of his muscles is 20%, how much energy does he need to obtain from food in order to do this?
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Physics Dept.
Worksheet for unit -2-
Grade 11A
Name:……………………………………………...
Efficiency and Energy loss) Continue)
η: - called eita
η = (useful output Energy / total input Energy) x 100 %
Or η = (useful output power / total input power) x 100 %
As we see in these figures not all energy input can be used but there is lost amount in form of heat.
Problems
1. Calculate the efficiency of a radio that gives of 30J of sound from 360J of electrical energy
2. If the efficiency of a device is 64 %, what is the amount of Energy lost by this device??
3. What is the amount of energy wasted by the motor?
4. Calculate the efficiency of a runner who produces of 500J of kinetic energy from 2500J of chemical energy
from food.
5. The efficiency of an electric lamp is 25%. If it receives 100J per second of electrical energy, how
much of this is transferred as light energy?
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Physics Dept.
Worksheet for unit -2-
Grade 11A
Name:……………………………………………...
Efficiency and Energy loss) Continue)
1) An electric motor pulls a mass of 4kg up by 3 m in 5 seconds when supplied with 360J of
electrical energy.
a) What is the weight of the mass?
b) How much work does the motor do?
c) What is the power of the motor?
d) What is the power supplied to the motor?
e) What is the percentage efficiency of the motor?
2) A light bulb is rated as 40W
a) How much electrical energy does this bulb use in one second?
b) Calculate the efficiency of the bulb if it gives out 5J of light in one second.
c) d) What is the useful power output of the light bulb?
d) (e) How much light energy should the bulb give out in 3 minutes?
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