Class 9 Exam > Class 9 Videos > Numerical - Work & Energy, Force & Laws of Motion, Force & Laws of Motion, Science, Class 9
Numerical - Work & Energy, Force & Laws of Motion, Force & Laws of Motion, Science, Class 9 Video Lecture
FAQs on Numerical - Work & Energy, Force & Laws of Motion, Force & Laws of Motion, Science, Class 9 Video Lecture
| 1. What is work and energy? |  |
Ans. Work is defined as the transfer of energy that occurs when a force is applied to an object and the object moves in the direction of the force. Energy, on the other hand, is the ability to do work. It exists in different forms such as kinetic energy (energy of motion), potential energy (stored energy), thermal energy (heat energy), etc.
| 2. What are the three laws of motion? | |
Ans. The three laws of motion, formulated by Sir Isaac Newton, are as follows:
1. Newton's First Law of Motion: Also known as the law of inertia, it states that an object at rest will remain at rest, and an object in motion will continue to move with a constant velocity unless acted upon by an external force.
2. Newton's Second Law of Motion: It states that the force acting on an object is equal to the mass of the object multiplied by its acceleration. Mathematically, F = ma.
3. Newton's Third Law of Motion: It states that for every action, there is an equal and opposite reaction. In other words, whenever one object exerts a force on a second object, the second object exerts an equal and opposite force on the first object.
| 3. What is the relation between force and motion? | |
Ans. Force and motion are directly related. Force is what causes an object to move or change its motion. According to Newton's second law of motion, the force acting on an object is directly proportional to its mass and acceleration. When a force is applied to an object, it accelerates or decelerates depending on the direction of the force. In the absence of any external force, an object will continue to move with a constant velocity.
| 4. How is momentum related to force and motion? | |
Ans. Momentum is the product of an object's mass and velocity. It is a vector quantity that represents the quantity of motion an object possesses. According to Newton's second law of motion, the rate of change of momentum of an object is equal to the net force applied to it. Mathematically, force (F) is equal to the change in momentum (Δp) divided by the change in time (Δt), or F = Δp/Δt. This shows that a force is required to change the momentum of an object, and the greater the force applied, the faster the change in momentum.
| 5. How does work and energy relate to force and motion? | |
Ans. Work and energy are related to force and motion. When a force is applied to an object and the object moves in the direction of the force, work is done. The amount of work done is equal to the product of the force applied and the displacement of the object in the direction of the force. This work done results in a change in the object's energy. If the force is applied in the direction of motion, the work done increases the object's kinetic energy. If the force is applied opposite to the direction of motion, the work done decreases the object's kinetic energy. Therefore, work and energy play a crucial role in describing and understanding the relationship between force and motion.
Text Transcript from Video
hello friends this video on force and
laws of motion part 9 is brought to you
by exam feel calm no more flow from exam
let's look at problem number 10 it says
an object of mass hundred kg is
accelerated uniformly from a velocity of
5 meter per second to 10 meter to 8
meter per second in 6 seconds ok so you
have an object of mass hundred kgs so
initial velocity was 5 meter per second
final velocity is 8 meters per second
and in Hauenstein this increase in
velocity took place six seconds so we
have to calculate the initial momentum
we have to also calculate the final
momentum and we also have to calculate
the magnitude of the force so what would
be the initial momentum mass into
velocity mass into initial velocity
rather so that will be equal to hundred
into 5 that is equal to 500 kg meter per
second now let us calculate the final
momentum which will be equal to mass
into final velocity which is equal to
hundred into 8 that is equal to 800 kg
meter per second then we have to
calculate the force exerted so force is
given by mass into acceleration so
masses give an acceleration is not even
so for acceleration we will make use of
the first equation of motion that is V
is equal to u plus 80 so from this we
can say a is equal to B minus 2 divided
by T that is equal to eight minus five
divided by six which is equal to zero
point five meter per second square so
therefore force is equal to mass into
acceleration which is equal to hundred
into zero point five that is equal to 50
Newtons so this is the magnitude of the
force exerted on the object let us look
at problem 11 it says how
much momentum will add um day of mass 10
kgs transfer to the floor if it falls
from a height of 80 centimeters take its
downward acceleration to be 10 meter per
second squared
so in this case the mass of the dumbbell
is given as 10 kgs it falls from a
height of 80 centimeters that means the
distance that it covered is 80
centimeters which is equal to 0.8 meters
what is the acceleration of the dumbbell
it is 10 meter per second square initial
velocity is equal to zero and we have to
calculate the final velocity because we
have to calculate how much momentum will
it transfer to the floor that means it
will transfer to the floor only when it
will reach the floor that means the
final velocity we should know only then
we can calculate the momentum so how do
we calculate the final velocity using
the third equation that is v square is
equal to u square plus 2 a s so from
this we can say v square is equal to 0
plus 2 into a into S so this is equal to
16 so V is equal to 4 meter per second
so this is the velocity when it reaches
the floor therefore the momentum that it
will transfer to the floor will be equal
to the product of mass and velocity so
mass is 10 kgs and velocity is 4 meter
per second so this would be 40 kg meter
per second right the problem seems to
persons managed to push a motor-car
of mass 1,200 kg at a uniform velocity
along 11 wrote the same motor-car can be
pushed by 3 persons to produce an
acceleration of 0.2 meter per second
square with what force does each person
push the motor-pod
so what's happening here it is suppose
you have this motor guy so in the first
things there are 2 persons who are
trying to push this motor guy right
such that this motor car of mass 1,200
kg is moving at a uniform velocity along
this road right in the second so this is
my personal in the second scenario what
happens the same motor car is now being
pushed by three persons right to produce
an acceleration of 0.2 meter per second
square now in the first case it was
moving with a uniform velocity that
means acceleration was zero but in this
case when three people are giving force
to this or it when three people are
trying to push this motorcar in this
case the acceleration is 0.2 meter per
second square
so we have to find out the force that
each person is with which each person is
pushing the motor back so let us first
consider case 1 in the first case what
happens here force given by two people
since then net acceleration is zero what
does that mean the net force acting on
this motor car is equal to zero like
that's what we study from second
newton's second law we know that if
acceleration is zero your net force has
to be zero net force zero means the
total force given by these two persons
will be content will be equal and
opposite to the force of friction which
is acting in the opposite direction like
so we can say that force given by two
persons will be equal to the force of
friction which will be exerted by the
road on the vehicle right in the second
case what happens in the second case the
force given by three people is greater
than the force of friction
now since this force is greater than the
force of friction that is why the motor
vehicle is moving with some acceleration
that means it's velocity is increasing
right so that means this force given by
three people is great and by greater
than the force of friction now by how
much this force is greater but than the
force of friction so you can say that F
minus the frictional for
is equal to the net force that is acting
on this vapor so that will be equal to
mass of the vapor into the acceleration
of the vapor right what is the mass of
the vapor it is given as 1,200 kg and
what is the acceleration the
acceleration produced in this case is
0.2 meter per second square so this
comes out to be 240 Newton's so that
means this 240 Newton is the extra
amount of force which has been provided
in case 2 now in case to what was the
extra thing one person was extra like
that means each person applies and in
the first part it says that each of the
persons are giving the same amount of
force that's what is mentioned in the
problem that assume that all persons
push the motor car with the same
muscular effort therefore we can say
that each person pushes the motor car
with a force of 240 Newton's and you
understood the difference in the first
case two people were there in the second
case three people were there but because
of this extra one person the motor car
is moving with an acceleration of 0.2
meter per second square so in this extra
force which is given by this one person
is mass into acceleration which is equal
to 240 Newton's so we can say that each
person is giving a force of 240 Newton's
thank you please visit exam viacom to
watch free educational videos try 3
online tests get the best quality study
materials study from the best tutors and
mentors and much more thank you once
again
laws of motion part 9 is brought to you
by exam feel calm no more flow from exam
let's look at problem number 10 it says
an object of mass hundred kg is
accelerated uniformly from a velocity of
5 meter per second to 10 meter to 8
meter per second in 6 seconds ok so you
have an object of mass hundred kgs so
initial velocity was 5 meter per second
final velocity is 8 meters per second
and in Hauenstein this increase in
velocity took place six seconds so we
have to calculate the initial momentum
we have to also calculate the final
momentum and we also have to calculate
the magnitude of the force so what would
be the initial momentum mass into
velocity mass into initial velocity
rather so that will be equal to hundred
into 5 that is equal to 500 kg meter per
second now let us calculate the final
momentum which will be equal to mass
into final velocity which is equal to
hundred into 8 that is equal to 800 kg
meter per second then we have to
calculate the force exerted so force is
given by mass into acceleration so
masses give an acceleration is not even
so for acceleration we will make use of
the first equation of motion that is V
is equal to u plus 80 so from this we
can say a is equal to B minus 2 divided
by T that is equal to eight minus five
divided by six which is equal to zero
point five meter per second square so
therefore force is equal to mass into
acceleration which is equal to hundred
into zero point five that is equal to 50
Newtons so this is the magnitude of the
force exerted on the object let us look
at problem 11 it says how
much momentum will add um day of mass 10
kgs transfer to the floor if it falls
from a height of 80 centimeters take its
downward acceleration to be 10 meter per
second squared
so in this case the mass of the dumbbell
is given as 10 kgs it falls from a
height of 80 centimeters that means the
distance that it covered is 80
centimeters which is equal to 0.8 meters
what is the acceleration of the dumbbell
it is 10 meter per second square initial
velocity is equal to zero and we have to
calculate the final velocity because we
have to calculate how much momentum will
it transfer to the floor that means it
will transfer to the floor only when it
will reach the floor that means the
final velocity we should know only then
we can calculate the momentum so how do
we calculate the final velocity using
the third equation that is v square is
equal to u square plus 2 a s so from
this we can say v square is equal to 0
plus 2 into a into S so this is equal to
16 so V is equal to 4 meter per second
so this is the velocity when it reaches
the floor therefore the momentum that it
will transfer to the floor will be equal
to the product of mass and velocity so
mass is 10 kgs and velocity is 4 meter
per second so this would be 40 kg meter
per second right the problem seems to
persons managed to push a motor-car
of mass 1,200 kg at a uniform velocity
along 11 wrote the same motor-car can be
pushed by 3 persons to produce an
acceleration of 0.2 meter per second
square with what force does each person
push the motor-pod
so what's happening here it is suppose
you have this motor guy so in the first
things there are 2 persons who are
trying to push this motor guy right
such that this motor car of mass 1,200
kg is moving at a uniform velocity along
this road right in the second so this is
my personal in the second scenario what
happens the same motor car is now being
pushed by three persons right to produce
an acceleration of 0.2 meter per second
square now in the first case it was
moving with a uniform velocity that
means acceleration was zero but in this
case when three people are giving force
to this or it when three people are
trying to push this motorcar in this
case the acceleration is 0.2 meter per
second square
so we have to find out the force that
each person is with which each person is
pushing the motor back so let us first
consider case 1 in the first case what
happens here force given by two people
since then net acceleration is zero what
does that mean the net force acting on
this motor car is equal to zero like
that's what we study from second
newton's second law we know that if
acceleration is zero your net force has
to be zero net force zero means the
total force given by these two persons
will be content will be equal and
opposite to the force of friction which
is acting in the opposite direction like
so we can say that force given by two
persons will be equal to the force of
friction which will be exerted by the
road on the vehicle right in the second
case what happens in the second case the
force given by three people is greater
than the force of friction
now since this force is greater than the
force of friction that is why the motor
vehicle is moving with some acceleration
that means it's velocity is increasing
right so that means this force given by
three people is great and by greater
than the force of friction now by how
much this force is greater but than the
force of friction so you can say that F
minus the frictional for
is equal to the net force that is acting
on this vapor so that will be equal to
mass of the vapor into the acceleration
of the vapor right what is the mass of
the vapor it is given as 1,200 kg and
what is the acceleration the
acceleration produced in this case is
0.2 meter per second square so this
comes out to be 240 Newton's so that
means this 240 Newton is the extra
amount of force which has been provided
in case 2 now in case to what was the
extra thing one person was extra like
that means each person applies and in
the first part it says that each of the
persons are giving the same amount of
force that's what is mentioned in the
problem that assume that all persons
push the motor car with the same
muscular effort therefore we can say
that each person pushes the motor car
with a force of 240 Newton's and you
understood the difference in the first
case two people were there in the second
case three people were there but because
of this extra one person the motor car
is moving with an acceleration of 0.2
meter per second square so in this extra
force which is given by this one person
is mass into acceleration which is equal
to 240 Newton's so we can say that each
person is giving a force of 240 Newton's
thank you please visit exam viacom to
watch free educational videos try 3
online tests get the best quality study
materials study from the best tutors and
mentors and much more thank you once
again
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