This worksheet 13 contains questions based on Chapter 13 Work and Energy with complete answers.
This
post explains the answers of questions given in the worksheet including
explanation, diagrams. These solutions will help you complete your assignments
and TMA also.
Work and Energy Worksheet 13 Solution
A
complete solution of Questions given in the worksheet 13 of Work and Energy of
NIOS Class 10 Science.
Q1.
Work is common term we use in our day-to-day
conversations. Ordinarily we include standing, reading, lying etc. in the
category of work. But in science, work has a very specific meaning- Define work
in terms of science with examples from day-to-day life.
Answer
According
to Science- work is said to be done when force is applied on a body and body
moves through some distance in the direction of force.
Work
is measured as the product of force and the displacement in the direction of
the force.
Examples
of Work from day-to-day life
1. When
we try to push a wall but displacement is zero so work is not done.
2. A
person carrying a heavy load on his head and walking does no work against
gravity because the displacement is horizontal but the force of gravity is
vertical.
3. When
a person climbs up a staircase, he moves upward against the force of gravity so
work is done.
Q2.
Calculate the work done by the force if the force
and displacement are perpendicular to each other. A man is carrying a bag of
4kg mass on his head and moves 1km on a levelled road. Calculate the work done
against the gravitational force. (g =10ms-2)
Answer
Given
values
Mass
of bag (m) = 4 kg
Distance
covered horizontally (s) = 1 km= 1000m
Acceleration
due to gravity (g) = 10 m/s2
Weight
(force of gravity) W= 4 ×10 =40N
Solution
Since
force is vertical and displacement is horizontal and they are perpendicular so
work done is zero.
W=0
Q3.
Derive a relationship between work, force and
displacement. Calculate work done if a body of 5kg is raised to 2m.
Answer
Work
is defined as the product of force and the displacement in the direction of the
force.
If
Force
applied on a body =F
Displacement
of the body = s
So
Work
= Force × Displacement
W=
Fs
Numerical
Problem
Given
Mass
(m) = 5 kg
Height
(h) = 2m
Acceleration
due to gravity (g) = 10m/s2
Find
force
F=
mg
= 5× 10 = 50N
Find
work
W=
F × s
= 50 × 2 = 100 J
Q4. It is observed that when one does work, she/he spends energy and more energy is required to do more work. Define energy. Is it practical 100% conversion of energy?
a) If yes, support your answer with reasons
b) If No, support your answer with reasons
Answer
Definition
– The capacity of a body to do work is determined by ‘energy’.
Is
100% conversion of energy practical?
No.
100 % conservation of energy is not possible.
Reason
In
the process of conversion of energy, some energy is remained unused or may be
wasted, so 100% conversion of energy is practically not possible.
Some
energy is lost in the form of heat, sound or friction.
Q5.
You do work by spending muscular energy which you
gain from the chemical energy of the food you eat. Your fan runs on electrical
energy. While playing with magnets you might have seen that a magnet attracts a
piece of iron because it has magnetic energy. This energy is available to us in
many different forms; observe your surroundings and explain different forms of
energy and their importance and limitations.
Answer
1. Mechanical
energy
The energy in the body possesses by virtue of its position or by virtue of its motion. This energy of two types- (i) Potential energy (ii) Kinetic energy
a. Potential energy
The energy possessed by a body due to
change in its position is called potential energy.
Ep
= mgh
b. Kinetic energy
Kinetic
energy is the capacity of doing work that a
body has by virtue of its motion.
Importance
i. Helps us do physical work
ii. Machines use mechanical energy to perform tasks.
iii. Moving vehicles, blowing wind all work due to mechanical energy
Limitations
i. It cannot be stored for long time.
ii. It is lost as heat due to friction.
iii. Requires some physical process to convert into useful work.
2. Thermal
energy
The
energy which flows in out body to give us sensation of hotness and out of our
body to give us sensation of coldness.
Importance
i. Keeps us warm
ii. Used in cooking food and heating water
iii. Used in industries for producing steam and running turbines.
Limitations
i. Heat is lost to the surroundings
ii. Difficult to convert all heat into work.
3. Light
energy
The
form of energy which enables us to see things is called light energy.
Importance
i. Helps plants in photosynthesis
ii. Used on solar plants to generate electricity.
Limitations
i. Sunlight is not available at night
ii. Intensity of sunlight depends on weather.
4. Electrical
energy
This
energy is generated due to movement of charged particles. It is used in
lighting bulbs, runs our fans.
Importance
i. Used to run appliances like fan, refrigerator and lights etc.
ii. Easily converted into other forms of energy like light, heat, mechanical etc.
Limitations
i. Requires power plants to generate electricity.
ii. Requires proper infrastructure to transport to remote areas.
5. Magnetic
energy
Magnet
attract a piece of iron and has ability to do work. The energy involve in the
functioning of a magnet is called magnetic energy.
Importance
i. Used in motors, generators, speakers, etc.
ii. Allow magnet to attract irons objects.
Limitations
i. Works in particular materials like iron, nickel and cobalt.
ii. Magnetic field become weak with distance.
6. Sound
energy
The
form of energy which enables us to hear is called sound. Sound originates when
a body vibrates and produces waves that travel to our ear through a medium.
Importance
i. Helps in communicate.
ii. Used in microphones, musical instrument, sonar etc.
Limitations
i. It needs a medium to travel.
ii. Create noise pollution.
7. Nuclear
energy
This energy is released in a nuclear reaction
by conversion of mass into energy. This is a non-conventional form of energy.
Importance
i. Produces large amount of energy from small amounts of fuel
ii. Used in nuclear power plants and medical treatment.
Limitations
i. Produce harmful radioactive waste.
ii. Requires high safety standards to avoid accidents.
iii. Costly technology
Q6.
Continue to Q5 we know the various forms of energy
get converted from one form to another in different situations. Name and
explain the law which states this phenomenon of converting one form of energy
to another form. Observe your surroundings and give some examples of energy
transformation from daily life.
Answer
Law
of conversion of energy
Energy
can neither be created nor be destroyed. It can only be transformed from one
form to another but total energy always remains constant.
Examples
of energy transformation from daily life
We
can easily see and understand the energy transformation in our daily life. The
following table will explain this.
|
Device/phenomena
|
Energy
transformation |
|
Electric
bulb |
Electric
energy to light energy |
|
Electric
heater |
Electric
energy to heat energy |
|
Solar
panel |
Light
energy to electric energy |
|
Microphone
|
Sound
energy to electric energy |
|
Loudspeaker
|
Electric
energy to sound energy |
|
Washing
machine |
Electric
energy to mechanical energy |
|
Photosynthesis
|
Light
energy to chemical energy |
|
Burning
of fuel |
Chemical
energy to heat energy |
Q7.
Work is measured as the product of force and
displacement in the direction of the force but we did not consider whether the
work is done in one second or in one hour. However, the time taken to perform a
particular work is important, in our daily life. Why it is important to know
the rate at which work is done and how will you calculate the rate at which
work is done?
Answer
Work
depends on force and displacement in physics but this does not tell us how fast
the work is done. But in daily life time is very important.
Why
Rate of doing work is important
In
daily life, we often need to know how fast a machine or person can perform work
with efficiency and in less time.so the rate of doing work is very important.
The
rate of doing work helps us compare efficiency, speed and performance of
people, machines and devices.
Calculation
of the rate of work
The
rate of doing work is called power.
SI
unit of power is Watt (1 Joule/sec)
Q8. Two objects of mass 10kg and of mass 3.5kg are dropped simultaneously from a tower. Will they have the same acceleration, when they are 10m above the ground?a) If yes, support your answer with reasons
b) If yes, support your answer with reasons
Answer
Yes
, both objects will have same acceleration.
Reason
When
an object falls freely, gravitational force acts on it.
Gravity
pulls all objects towards the Earth with the same acceleration. This
acceleration is called ‘g’.
g= 10m/s2
gravity
does not depend on the mass of the object. So both 10kg and 3.5kg objects will
fall with the same acceleration of 10m/s2.
Q9.
Why road accidents at high speed are much worse
than the accident at low speeds?
Answer
Accidents
at high speed are more dangerous because high speed give the vehicle more
kinetic energy and this energy cause greater damage during collision.
This
means when the speed increases, the kinetic energy increases that cause great
damage.
Q10.
The velocity of a rocket is suddenly triple.
Calculate the ratio of two kinetic energies, if rocket’s initial velocity is v.
Answer
`K.E.=\frac{1}{2}mv^2`
Let
Initial velocity =v
Final velocity =3v
So initial kinetic energy
`K_1=\ \frac{1}{2}mv^2`
Final kinetic energy
`K_2=\ \frac{1}{2}m(3{v)}^2`
`K_2=\ \frac{1}{2}m9v^2`
`K_2=9(\frac{1}{2}mv^2)`
`K_2=9K_1`
So, the ratio of two kinetic energies
`K_1:K_2=1:9`
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