Work, Energy and Power
# Work: Work is said to be done if force acting on an object
displaces it in the direction of force.
For example: Lifting an object and keeping on
table, pulling an object through certain distance, etc.
# Energy: Energy is defined as the capacity to do work. Its SI unit is Joule (J).
Types of energy:
§ Mechanical
energy: The
sum of the potential and kinetic energy of the body is called mechanical
energy.
§ Electrical
energy: The
flow of electrons through a conductor is called electrical energy.
§ Heat
energy: The
energy produced from the molecular vibration of an object is called heat
energy.
§ Sound
energy: The
energy produced due to the vibration of an object is called sound energy.
§ Chemical
energy: The
energy produced due to the chemical change of a substance is called chemical
energy.
§ Magnetic
energy:
§ Nuclear
energy: The
energy which is obtained by splitting of heavy nucleus of an atom or Combining
light nuclei together is called nuclear energy.
§ Kinetic
energy: The
energy possessed by a moving body is called kinetic energy. Eg; fired bullet,
moving vehicle.
§ Potential
energy: Energy
possessed by a body due to its position or configuration is called potential
energy. Eg; compressed spring, stretched wires.
#Power: The rate of doing work is called power. Its SI unit is
watt.
1) What do you mean by 1 joule work? What do you
mean by 60 Watt written in an electric bulb?
Ans: 1J work is said to be done if a certain
object moved through a distance of 1 meter by applying 1N of force.
60W written in an electric bulb means that 60
joule of electrical energy is converted into heat and light energy in 1 second
by that bulb.
2) Write any two differences between Kinetic energy and Potential energy.
Ans:
|
S.No |
Kinetic Energy |
Potential Energy |
|
1 |
It is the energy possessed by a moving body. |
It is the energy possessed by position of a body. |
|
2 |
P.E.=mgh |
K.E. = 1/2m2; |
3) Write
the differences between energy and power.
Ans: The differences between energy and power are as follows;
|
S.No |
Energy |
Power |
|
1 |
Capacity to do work is called energy. |
Rate of doing work is called power. |
|
2 |
Its SI unit is Joule. |
Its SI unit is Watt. |
4) Name the
energy contained by the given actions:
a) Water collected on a dam = Potential energy
b) Stretched rubber = Potential energy
c) Burning match stick = Heat/Light energy
d) Moving fan = Kinetic energy
e) Glowing electric bulb = Heat/Light energy
f) A fallen stone = Potential/Kinetic energy
g) Bread = Chemical energy
h) Foot lifted to kick the football = Potential
energy
i) Blowing air = Kinetic energy
j) A bullet fired from a gun = Kinetic energy
5) What is
power? Give the value of 1H.P. in watt.
Ans: The rate of doing work is called power.
1 H.P = 746 W
) What is 1
Watt power?
Ans: If 1 joule of work is done in 1 second then
it is said to have 1 W power.
7) What do you mean by “Law of conservation of
energy”?
Ans: According to the Principle of conservation
of energy, “energy can neither be created
nor be
destroyed but can only be transformed from one form to another.”
8) What do you mean by transformation of energy?
Ans: The process of changing one form of energy
to another is known as transformation of energy.
9) What is 1N
force?
Ans: If an object of 1 kg mass is used to move with an acceleration of 1 m/s2 then 1 N force is said to be applied.
10) What are the two factors that affect the
kinetic energy of a body?
Ans: Factors affecting kinetic energy of a body are;
a) mass of an object.
b) velocity of moving
object.
11) What are the sources of electrical energy.
Ans: Dynamo, cell, generator, photo cell, etc are the sources of electrical
energy.
12) What are the different uses of magnetic
energy?
Ans: The different uses of magnetic energy are;
a) It is use to lift heavy metallic
loads.
b) It is used to produce
electricity.
c) It is sued to produce sound
energy as in radio, television etc.
13) Define
work and power. Write the relation between them.
Ans: Work is said to be done if force acting on
an object displaces it in the direction of force.
The rate of doing work is called power.
14) Write any two application of electrical energy.
Ans:
§
Electrical
energy can be used in trolley buses.
§
All
electrical appliances consume electrical energy.
15) Define Kinetic energy and Potential energy.
Ans:
Kinetic energy:
The energy possessed by a moving body is called
kinetic energy. Eg; fired bullet, moving vehicle.
Potential energy:
Energy possessed by a body due to its
position or configuration is called potential energy. Eg; compressed spring,
stretched wires.
16) Priya is standing on the road for 3 hours by
carrying a load of 100N. What is the work done by her?Why?
Ans:
Work done is equal to Zero because the
displacement is zero.
Numerical
Problems:
Q1) If a
man of mass 80 kg climbs a hill of height 900 m in 30 minutes, calculate his
power?
Ans:
|
Soln: |
Q2)
Calculate the power of the man who lifts 175 N of load to 25 m height in 100
seconds.
Ans:
|
Soln: |
Q3) Calculate the power of crane if it lifts a
car of mass 2500 kg up to 9 m high at 5 seconds.
Ans:
Here;
Mass (m) = 2500 kg
Distance (d ) = 9 m
Time (t) = 5 sec.
Power (p) = ?
Now, we have;
p = work done/ time taken
p = (m x d x g)/t .......................................(since,
work done = m x d x g)
p = (2500 x 9 x 9.8)/5
................................(since, g = 9.8m/s^2)
p = 220500/5
p = 44100 Joule.
Therefore, the power of crane is 44100 J.
Label: work energy and power, science8, science 8, work, energy, power, watt, 1joule work, types of energy,