Edexecl physics For grade 10 to solve problems in paper1

WORK
●If an object or system,
such as your body,
exerts a force on an
object and that force
causes the object’s
position to change, you
are doing work on the
object.

When a physicist is talking about work, he
mainly talks about a force causing a
displacement of an object in the same action
of line.
W=F.Δx
W = work = joule (J) (N.m=J)
Δx = displacement = meter (m)
F = force applied = newton (N)

example
Work done by 8N between KL is 2 joule. Then, what is the
distance x?

example
a.What is the work done by friction force?
b.What is the work done by F1?

example
Friction force between KL is 8N and between LM is 6 N.
If the work done between KL and LM are equal, find the
distance between LM.

example
Net work done to 2 kg object is 6,4 j. What is the force of
friction?

POWER
●Power is the measure for how fast the work is
done.
m/s
Average
velocity
Vave
J/s = W (watt)
power
P
s
time
t
J
work
W
Unit
Quantity
Symbol

example
●A horse is pulling a cart with a force of 150 N
by 10m is 20 s

example
●A man lifts a weight of 300N through a vertical
line with an average velocity of 1m/s. What is
the power of the man?

ENERGY
●Energy is defined as “ability to
do work”
●We do work by using energy so
both work and energy are
measured in joules.

Edexecl physics For grade 10 to solve problems in paper1

The Law of Conservation of
Energy
●The energy in a system
may take on various forms
such as thermal, light,
electric, etc… but the
energy may neither be
created nor destroyed.
●Therefore the sum of all
energies in the system is a
constant.

Mechanical Energy
●Ability to do work in a
system.
●It has two categories
which are kinetic
energy and potential
energy

Kinetic energy
●Kinetic energy is the energy of motion. An
object which has motion - whether it be vertical
or horizontal motion - has kinetic energy.
●Kinetic energy is a scalar quantityKinetic
energy is a scalar quantity; it does not have a
direction unlike velocityKinetic energy is a
scalar quantity; it does not have a direction
unlike velocity, accelerationKinetic energy is a
scalar quantity; it does not have a direction
unlike velocity, acceleration, force

where m = mass of object
v = speed of object
●Kinetic energy depends upon two variables:
the mass (m) of the object and the speed (v) of
the object.
where m = mass of object
v = speed of object

example
●Determine the kinetic energy of a
1000-kg roller coaster car that is
moving with a speed of 20.0 m/s.

example
●If the roller coaster car in the above
problem were moving with twice the
speed, then what would be its new
kinetic energy?

example
What is the ratio of the objects’
kinetic energies?

Potential Energy
●An object can store energy as the result of its
position.

Gravitational potential energy
●Gravitational potential energy is
the energy stored in an object as
the result of its vertical position
(i.e., height).
●The energy is stored as the
result of the gravitational
attraction of the Earth for the
object.
●PEgrav = mass . g . height
●PEgrav = m . g . h

Work-Energy Principle
●The net work (Wnet)done on an object is equal
to the change in the kinetic energy (ΔKE) of the
object.
Fnet. Δx=1/2mv2
final-1/2mv2
initial
Fnet. Δx=KEfinal-KEinitial
Wnet= ΔKE

Work done by friction force
●Force of friction
between LM is 20N.
How many meters
does object moves
before it stops?

Ex:
●5N of Ff is acted on the object for 4m. If mass
of the object is 2kg, find its velocity at point L.

Elastic Potential Energy
●Elastic potential energy is the energy stored
in elastic materials as the result of their
stretching or compressing.
●Ex: rubber bands
●bungee chords
●Trampolines
●Springs
●an arrow drawn into a bow

●Conservation of energy in spring

Ex:
●What is the elastic potential energy stored in a
spring which is compressed 10 cm and whose
spring constant is 800 N/m.

Thermal Energy
●Temperature is not energy.
●Temperature is related to the average
kinetic energy of the molecules of a substance.

●Temperature is defined as a measure of
average kinetic energy of that make up the
object. So, it does not depend the number of
particles or size of the matter.
●Temperature can be measured in a variety of
units.Celcius,fahrenheit and kelvin.

Thermometer
1)Metal thermometers:
●Temperature variations are indicated by the
changes in length of one or more metal rods.
●A bimetallic strip thermometer ; The strip
consists of two metals which expand at
different rates as they are heated (steel and
copper.)

2)Liquid thermometers
A liquid (usually mercury or alcohol) is sealed
into a glass capiilary tube having a bulb at one
end. When temperature is increased, both
liquid and tube expands.

Why isn't water used as the
liquid in the common
thermometer?
●If waterIf water was used in the common
liquid thermometer we wouldn't be able to
measure anything over 100 °C (212 °F) or
under 0°C (32 °F).

●3) Electronic thermometers:
●It uses thermoresistor to measure
temperature.

C-0 F-32 K-273 X-FP
= = =
100-0 212-32 373-273 BP-FP
C-0 F-32 K-273 X-FP
= = =
100 180 100 BP-FP

HEAT
●Heat is a measure of how much thermal
energy is transmitted from one body to another.
●We cannot say a body “has” a certain amount
of heat any more than we can say a body “has”
a certain amount of work.
●While both work and heat can be measured in
terms of joules, they are not measures of
energy but rather of energy transfer.

●A hot water bottle has a certain amount of
thermal energy; when you cuddle up with a hot
water bottle, it transmits a certain amount of
heat to your body.

Specific Heat
●Specific heat measures how much heat is
required to raise the temperature of a certain
mass of a given substance.
●Every substance has a different specific heat,
but specific heat is a constant for that
substance.

●The specific heat of water is 1 calorie/gram °C
= 4.186 joule/gram °C which is higher than any
other common substance.

●The relationship does not apply
if a phase change is
encountered, because the heat
added or removed during a
phase change does not change
the temperature.

ex:
●Some amount of heat is given to 20g of water
at 30°C, the final temperature of water is 50 °C.
Find the amount of heat given to water.
(cwater=1cal/g °C)

Ex:
●When 500g of a substance absorbs 1000 cal
of heat, its temperature rises from 20 °C to 25
°C. What is the specific heat of substance?

Ex:
●How many kilocalories are needed to increase
the temperature of 2 kg of aluminium from 20
°C to 80°C? (cAl=0,22 cal/g °C)

●Specific heat of the substance is 0,2 cal/g °C.
Find m in grams.

●Temperature versus heat graph is given for
substances X and Y. Find the ratio of their
specific heats cx/cy.

Edexecl physics For grade 10 to solve problems in paper1

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