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JOHNSON FOUNDATION SCHOOL

Class 9 Physics Force Synopsis and Re!lar Assin"en# $% & '% & (''9

Par# A Synopsis o) Force

Force is either a push or a pull.

It can be defined as the external agency that changes or tends to change the state of rest or that ofuniform motion of a body moving in a straight line.

There two types of forces I) contact force II) Field force

The concept of field is important: A field is a region in which the body experiences a force as a result ofthe presence of some other body.

The application at a force leads to many changes. A stationary body can be set into motion, both the

speed and direction of a moving body are altered and a body can be deformed.

Newtons first law of motion: If the net force F exerted on an obect is !ero, the obect continues in

its original state of motion.

From the "stlaw of motion the concept of inertia was born. The tendency of a body to retain its originalstate of motion is called inertia.

A lot of interesting examples can be seen in the day#to#day life. $henever a dusty carpet is er%ed the

dust flies off & due to inertia.

'inear momentum of an obect with mass m and moving with a velocity v is defined by p ( mv

I units are is " *ewton second +* " *s ( " %gms#" +- unit is " dyne second

"dyne second ( " gcms#".

$hen a / g bullet hits a person with v ( /."ms #"no damage occurs, but if it hits with v ( "//// ms #"it

would be fatal. The reason is increased momentum.

Newtons 2ndlaw of motion: The acceleration of an obect is directly proportional to the net force

acting on it and is inversely proportional to the mass or F ( ma.

This law also be stated as 0 The rate of changes of linear momentum is directly proportional to the

impressed force and is in the same direction

I unit of force is p *ewton. " *ewton ( " %g ms#12 +- unit of force is dyne. " dyne ( " g cms#1

" * ( "/dynes.

I unit for gravitational unit of force is " %gf. Newtons 3rdlaw: If two obects interact, the force F"1exerted by obect " on obect 1 is e3ual in

magnitude but opposite in direction to force F1"exerted by obect 1 on obect ".

JOHNSON FOUNDATION SCHOOL

Class 9 Physics Force Synopsis and Re!lar Assin"en# $% & '% & (''9

Par# A Synopsis o) Force

Force is either a push or a pull.

It can be defined as the external agency that changes or tends to change the state of rest or that ofuniform motion of a body moving in a straight line.

There two types of forces I) contact force II) Field force

The concept of field is important: A field is a region in which the body experiences a force as a result of

the presence of some other body.

The application at a force leads to many changes. A stationary body can be set into motion, both the

speed and direction of a moving body are altered and a body can be deformed.

Newtons first law of motion: If the net force F exerted on an obect is !ero, the obect continues in

its original state of motion.

From the "stlaw of motion the concept of inertia was born. The tendency of a body to retain its originalstate of motion is called inertia.

A lot of interesting examples can be seen in the day#to#day life. $henever a dusty carpet is er%ed the

dust flies off & due to inertia. 'inear momentum of an obect with mass m and moving with a velocity v is defined by p ( mv

I units are is " *ewton second +* " *s ( " %gms#" +- unit is " dyne second

"dyne second ( " gcms#".

$hen a / g bullet hits a person with v ( /."ms #"no damage occurs, but if it hits with v ( "//// ms #"it

would be fatal. The reason is increased momentum.

Newtons 2ndlaw of motion: The acceleration of an obect is directly proportional to the net force

acting on it and is inversely proportional to the mass or F ( ma.

This law also be stated as 0 The rate of changes of linear momentum is directly proportional to the

impressed force and is in the same direction

I unit of force is p *ewton. " *ewton ( " %g ms#12 +- unit of force is dyne. " dyne ( " g cms#1

" * ( "/dynes.

I unit for gravitational unit of force is " %gf.

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Newtons 3rdlaw: If two obects interact, the force F"1exerted by obect " on obect 1 is e3ual in

magnitude but opposite in direction to force F1"exerted by obect 1 on obect ".

Par# * +N!"ericals,

$, +alculate the velocity of a body of mass /. %g when it has a linear momentum of *.

1) An electron of mass 4 x "/#5"

%g is moving with a linear velocity of 6 x "/7

ms#"

. +alculate the linearmomentum of electron.

5) A car initially at rest pic%s up a velocity of 71 %mh#"in 1/ seconds. If the mass of the car is "/// %g find a)Force developed by engine b)distance covered by car.

8) A force of // dynes acts on a mass of /./ %g over a distance of 1/ m. Assuming that the mass is initially at

rest, find the final velocity and time for which the force acts.) A force of 6// dynes acts on a glass ball of mass 1// g for "1 s, If initially the ball is at rest, find i) the final

velocity ii) distance covered.

6) A bullet of mass 5/ g and moving with a velocity x hits a wooden target with a force of "97. *. If the bulletpenetrates 9/ cm, find x.

7) A car of mass "/// %g develops a force of // over a distance 84 m. If u ( /, find i) and ii) time for

which it accelerated

Par# C +Reasonin,

-.plain #he )ollo/in0

") $hy do we er% wet clothes before placing them on a line;1) $hy does dust fly off, when we hit the carpet with a stic%.

5) $hy do fruits fall off when the branches sha%e;

8) $hy it is difficult to wal% on a marshy ground.) $hy it is dangerous to ump from a moving vehicle.

6) $hy does a boatman push water bac%wards with oasis while rowing a boat.

7)