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True Discount and Banker's Discount problems tricks in Hindi | fast track formulae for problem solving.


TRUE DISCOUNT 1). वास्तविक बट्टा = मिश्रधन - वर्तमान धन
2). यदि ब्याज की दर r% वार्षिक , समय t व वर्तमान धन (pw) है, तो वास्तविक बट्टा = PW×r×t/100
3). यदि r% तथा समय t के बाद देय धन A है, तो तत्काल धन pw = 100×A/(100+r.t)
4). यदि देय धन A पर r% व समय t दिए गए है, तो वास्तविक बट्टा = A.r.t /(100+r.t)
5). यदि किसी निश्चित समय के पश्चात निश्चित वार्षिक दर पर, देय धन पर वास्तविक बट्टा (TD) व समान समय व दर के लिए साधारण ब्याज (SI) हैं, तो देय धन A =      SI × TD/(SI - TD)
6). यदि t समय पश्चात r% वार्षिक दर पर, देय धन पर वास्तविक बट्टा (TD) व साधारण ब्याज (SI) है , तो -  SI - TD = TD×r×t/100
7). t वर्ष बाद r% चक्रवृद्धि दर पर देय धन A का तत्काल धन (PW) = A/(1+r/100)^t   व वास्तविक बट्टा = A - PW
BANKER'S DISCOUNT1). महाजनी बट्टा = शेष समय (समाप्त न हुए समय) के लिए बिल पर ब्याज = बिल की राशि × दर × शेष समय /100
2). महाजनी लाभ = महाजनी बट्टा - वास्तविक बट्टा
3). यदि बिल का मान / अंकित मूल्य A है, समय t व दर r% है, तो महाजनी बट्टा = A×r×t/100

GRAVITATION study notes for IIT JEE | concept booster , chapter highlights , LAWS OF NATURE



This laws states that every body in the universe attract another body with a force which is directly proportional to product of the their masses and inversely proportional to the square of distance between them act along the line joining the two bodies.
According to this law- 
F = GMm/r^2 , where G is the proportionality constant called universal Gravitational constant.
  1. This universal Gravitational constant G is a scaler quantity.
  2.  This constant remains same or unchanged in this entire universe , and it is independent of the shape , size and nature of the object and also independent of the intervening medium and temperature of the bodies.
  3. Value of G is in SI system is 6.67×10^-11Nm^2/kg^2. and value of G in CGS system is 6.67×10^-8^2/g^2
  4. Dimensional formula of G is[M^-1.L^3T^-2]
  5. Gravitational force between the two bodies is equal in magnitude but in opposite directions , hence it obeys the Newton's third law of motion. It forms action reaction pair.
  6. This is a type of conservative force , means work done by it is independent of path taken.
  7. It is central force because it acts along the line joining the centres of the two bodies.


Acceleration produced in the body due to Gravitational force is called acceleration due to gravity, Or in another word, It is the acceleration produced in the body which is falling free in the effect of gravity.
Acceleration due to gravity is denoted by small letter g and it's unit is m/s^2.
Mathematically it is given as-

      g = GMe/r^2. 
where Me is the mass of the earth and r is the distance of the body from the centre of the earth.
  1. If the body is on the surface of the earth then g is given as, g = GMe/Re^2.    Where Me is the earth's mass and r=Re is equal to radius of the earth.
  2. It is a vector quantity and it's dimensional formula is [M^0L^1T^-2]
  3. Value of g on the surface of the earth is taken as 9.8m/s^2.
  4. It's value can change with change of the altitude ,depth, shape and rotation of the body.
  5. Gravitational acceleration in the form of Gravitational constant is -.                            g = (4/3)πGReρ , where Re is the radius of the earth and ρ is the density of the earth.
  6. The value of acceleration due to gravity is independent of the shape, size and mass of the body, which is experiencing the Gravitational force. But it depends on the mass and radius of earth or any other planets which exerts Gravitational force.
  7. Acceleration due to gravity increased/decreased by 2n% on the surface of the planets, if their radius is decreased/increased by n% ,if their mass keeps unchanged.
  8. Acceleration due to gravity increased by n% on the surface of the planets, if their mass is increased by n% ,if their radius keeps unchanged.
  9. Acceleration due to gravity decreased by n% if the density of the planets decreased by n%, keeping the radius unchanged.



If we go high through the height h from the earth crust then the acceleration due to gravity starts decreasing.
At height h from the earth crust ADG is given as-
g(h) = GMe/(Re+h)^2 = g(1+h/Re)^-2 
If h<<<<Re then
 g(h) = g(1-2h/Re).   [g = GMe/Re^2]


When we go below towards the centre of the earth , acceleration due to gravity starts decreasing and it's become zero at centre.
It's again starts increasing if we starts to go towards the crust and it become maximum at the surface of the earth. So acceleration due to gravity at depth d is given as-

g(d) = GMe(Re-d)/Re^3 = g(1-d/Re)


If earth is rotating with angular velocity ω , then the acceleration due to gravity because of rotating of the earth at any latitude δ is given as-
      g(δ) = g-Reω^2.cos^2δ
The angular velocity(ω) of the earth is taken 7.3×10^-5rad/s.
  1. At the equator where δ is 0 , the  g(δ) is given as ,   g(δ)  = g - ω^2.Re
  2. At the poles , δ is 90° , the g(δ) is given as , g(δ) = g
  3. Difference between the acceleration due to gravity at poles and equator is -.   g(p)-g(e) = g-(g-Reω^2) = Reω^2


Earth is not a perfectly sphere , it is flattened at the poles and bulged at the equator as same like as an orange, due to this flatting the diameter of the earth is 21 km larger along with the equator as compared to diameter along with the poles. Both rotation and equatorial bulged contribute additively keeps the g smaller at the equator than the poles.


  1. Gravitational field is a space around a body in which if another body comes then it experiences a Gravitational pull.
  2. The Gravitational field intensity (E) at a distance r due to a point mass M is -.           E = GM/r^2 = Gravitational acceleration
  3. Gravitational field intensity is a vector quantity it always directed towards the centre of the mass which produces Gravitational the field.
  4. E become zero at infinity.
  5. Gravitational field intensity obeys the superposition principle ie. the total G-intensity(E) at a point is the vector sum of all the G-intensities acting at that point due to individual masses. ,                                    E = E1+E2+E3+......
  6. Gravitational field intensity due to a point mass is E = GM/r^2
  7. Gravitational field intensity due to uniform circular ring along it axis is ,.                        E = GMr/(r^2+R^2)^3/2 , where R is the radius of the ring and r is distance of the point from its centre.
  8. Gravitational field intensity due to a uniform disk at a point on its axis is.            E = (2GMr/R^2)[1/r - 1/√(r^2+R^2)].          In terms of θ is.                                      E = 2GM(1-cosθ)/R^2.           where R is the radius of the ring and r is distance of the point from its centre.
  9. Gravitational field intensity due to a solid sphere of radius R at any external point of distance r from its centre.                             E = GM/r^2 , and any internal point of distance r , E = GMr/R^3
  10. Gravitational field intensity due to uniform hollow sphere at any point inside the sphere is zero. And at any point outside the sphere of distance r is. ,E = GM/r^2


It is the amount of work done in bringing a body of unit mass from infinite to a point in Gravitational field of another body without any acceleration. 
Mathematically ;
                     V = W/m
  1. Gravitational potential at a point due to a point mass M is , V = -GM/r
  2. Gravitational potential due to uniform ring at a point along its axis is ,                                   V = -GM/√(R^2+r^2)
  3. Gravitational potential due to hollow sphere , outside the shell is V = -GM/r.     And inside the shell is V = -GM/R.   
  4. Gravitational potential V is a scalar quantity but potential gradient dV/dr is a vector quantity.       
  5. The relation between Gravitational potential and Gravitational intensity is.       E =-dV/Dr
  6. Gravitational potential obeys the superposition principle ie. The sum of all the Gravitational potential V at a point is sum of all the individual Gravitational potential which are acting at that point.                                      V = V1 +V2+V3+......
  7. Gravitational potential due to a uniform solid sphere of radius R , when the point is outside the sphere is.           V = -GM/r. and when the point is inside the sphere is.                                                V = -GM(3R^2 - r^2)/2R^3         


Gravitational potential energy is the amount of work done in bringing a body of unit mass in the Gravitational field of other body from infinite without any acceleration.
                   W = Vm
  1. Gravitational potential energy of a body of mass m which is r distance from the centre of mass M is, U = -GMm/r
  2. Work done in taking a body of mass m from the earth's surface to the height h , against the Gravitational pull is-.              W = ∆U = GMmh/R(R+h) , if h<<<R then the W = GMmh/R^2 = mgh , if h=R then the W = mgh/2



This laws states that, all planets moves in elliptical orbit with the sun situated at one of the foci of the ellipse.
This laws gives the geometry of planetary motion.


This laws states that , the speed of planets around the sun varies in such a way that the radius vector drawn from the sun to the planets sweep equal areas in equal interval of time.


This laws states that, the square of the time period of revolution of the planets around the sun is directly proportional to the cube of the semi major axis of the elliptical orbit.


It is the minimum speed with which a body is projected vertically upward from the surface of the earth , that it escaped out from the Gravitational pull of the earth and never will return. 
    Ve = √(2GM/R) , where M is the mass of the planet and R is the radius of that planet.
Ve = √(2G×volume×density/R) 
      = √[(2G/R)(4/3πR^3)ρ] =√[8πGR^2ρ/3]
  1. Escape velocity for earth is 11.2km/sec
  2. To throw a heavy or light object out of the earth you need same velocity.
  3. If the ratio of radii of two planets is r and the ratio of their acceleration due to gravity is a , then the ratio their escape velocity is   √ar.
  4. Escape velocity in the terms of g is-.             Ve = √2gr
  5. If radius of the earth is doubled keeping mass unchanged then the escape velocity become 1/√2 times the present value.


Satellite is a body , which is constantly revolving around a body(which is greater in size) in the fixed orbit.

If a satellite of mass m revolving around the planet of mass M at the height h from the surface, then the radius of the orbit is,                 r = R+h
Where R is the radius of the planet. The Gravitational force between m and M provide the necessary centripetal force for circular motion.


At which speed satellites revolve around the planets is called orbital velocity.
  1. Orbital speed is independent of the mass of the orbiting body and it is always directed along the tangent of the orbit.
  2. Orbital speed is given by Vo = √GM/(R+h). if h= 0 , means satellite is very close to the planet(earth) , then Vo = √GM/R = √gR                     = √10×6.4×10^6 = 8km/sec
  3. Orbital velocity in the terms of escape velocity is Vo = √2GM/2R = Ve/√2.                Ve = √2.Vo
  4. Orbital velocity vary near the surface of the earth and it is about 7.92Km/s
  5. If satellite altitude is n times the radius of the earth, then the orbital velocity is.    1/√(1+n) ,times orbital velocity near the earth surface.
  6. If satellite radius is n times the radius of the earth, then the orbital velocity will be     1/√n ,times the orbital velocity near the earth surface.


It is the time taken by the satellites to complete one revolution. It is denoted by T , it is given by
  T = 2πr/v = 2πr(√r/GM) 
After squaring both sides 

T^2 = (4π^2/GM)r^3, 

[ T^2 directly proportional to r^3 , Kepler's laws of period]
 The value of proportionality constant is 


Angular momentum is given as 
L= mvr = mr√GM/r = √m^2.GMr 

In the satellites motion the net force is centripetal force , and torque due to this force is zero about the centre of the orbit. So total angular momentum is conserved in this case.
L is constant.


The potential energy of the satellite is - 
U = mV = - GMm/r , the kinetic energy of the satellite is K.E = 1/2mVo^2 = GMm/2r
Total mechanical energy of the satellite is 
Total(energy) = - GMm/r +GMm/2r = -GMm/2r

The total energy is negative means satellite is bound to the planet with a attractive force and external energy is necessary to remove the satellite from the orbit to infinity.


It is the energy required to remove the satellite from the orbit to the infinity.
Binding energy, E = -GMm/2r



It is the type of satellites , which rotates in the same direction as earth rotates ie. West to east
Then the relative angular velocity of both bodies is zero. , ωs - ωe = 0.
So for a observer who is on the earth , satellite appears stationary, such satellite called geo-stationary satellite. The orbit of geo-stationary satellite is called parked orbit.
  1. Time period is T= 24 hours.
  2. Height of geo-stationary satellite is given as h = [T^2.GMe/4π^2]^1/3 - Re = 36,000km
  3. This types of satellites are used in radio communication, transmission of TV and telephone signals.


The satellites which revolve around the earth in circular motion from north to south orbit and passes over the north to south pole.
  1. It is low altitude satellite ~500-800km
  2. Angle of inclination from equatorial plane is 90°.
  3. They often are called sun synchronous satellite because it croses the earth equator daily at the same time.
  4. These satellites are used in remote sensing and meteorological research and enviromental studies.etc.


The radial acceleration of the satellite is given by ar = Fr/m = GMm/r^2.m = GM/r^2

For a astronaut in the satellite , his normal reaction N and his radial force m(a).a(r) balances the Gravitational force as follows
GMm/r^2 - N - m(a).a(r) = 0, or
GMm/r^2 - N - GMm(a)/r^2 = 0 , then N = 0
So a astronaut feel no gravity in the satellite.



Boat and stream short-tricks in Hindi | Fast track arithmetic formulae for competitive examination.

BOAT AND STREAM (नाव एवं धारा)
1). यदि शांत जल में नाव या तैराक की चाल x किमी/घंटा व धारा की चाल y किमी/घंटा है, तो धारा के अनुकूल नाव अथवा तैराक की चाल = (x+y) किमी/घंटा
2). धारा के प्रतिकूल नाव अथवा तैराक की चाल = (x-y) किमी /घंटा
3). नाव की चाल = (अनुप्रवाह चाल + उद्धर्वप्रवाह चाल)/2
4). धारा की चाल =  (अनुप्रवाह चाल - उद्धर्वप्रवाह चाल)/2
5). यदि धारा की चाल a किमी/घंटा है, तथा किसी नाव अथवा तैराक को उद्धर्वप्रवाह जाने में अनुप्रवाह जाने के समय का n गुना समय लगता है,(समान दूरी के लिए), तो शांत जल में नाव की चाल = a(n+1)/(n-1) किमी/घंटा
6). शांत जल में किसी नाव की चाल x किमी/घंटा व धारा की चाल y किमी/घंटा है, यदि नाव द्वारा एक स्थान से दूसरे स्थान तक आने व जाने में T समय लगता है, तो दोनो स्थानों के बीच की दूरी = T(x^2 - y^2)/2x km
7). कोई नाव अनुप्रवाह में कोई दूरी a घंटे में तय करती है, तथा वापस आने में b घंटे लेती है, यदि नाव कि चाल c किमी/घंटा है, तो शांत जल में नाव की चाल = c(a+b)/(b-a) km/h
8). यदि शांत जल में नाव की चाल a किमी/घंटा है, तथा वह b किमी/घंटा की चाल से बहती हुई नदी में गत…

Emergence of British East India Company as an Imperialist Political Power in India

Dynamically changing India during early eighteenth century had a substantially growing economy under the authority of Mughal emperor Aurangzeb. But after his demise in 1707, several Mughal governors established their control over many regional kingdoms by exerting their authority. By the second half of eighteen century, British East India Company emerged as a political power in India after deposing regional powers and dominating over Mughal rulers. The present article attempts to analyze the reasons for emergence of British East India Company as an imperial political power in India and their diplomatic policies of territorial expansion. In addition to this, I briefly highlighted the Charter Acts (1773, 1793, 1813, 1833 and 1853) to trace its impact on the working process of Company.Establishment of East India Company in India

In 1600, British East India Company received royal charter or exclusive license…

Three dimensional geometry (part-1) | study material for IIT JEE | concept booster , chapter highlights.


In the following diagram X'OX , Y'OY and Z'OZ are three mutually perpendicular lines , which intersect at point O. Then the point O is called origin.
In the above diagram X'OX is called the X axes, Y'OY is called the Y axes and Z'OZ is called the Z axes.
1). XOY is called the XY plane. 2). YOZ is called the YZ plane. 3). ZOX is called the ZX plane.
If all these three are taken together then it is called the coordinate planes. These coordinates planes divides the space into 8 parts and these parts are called octants.
COORDINATES  Let's take a any point P in the space. Draw PL , PM and PN perpendicularly to the XY, YZ and ZX planes, then
1). LP is called the X - coordinate of point P. 2). MP is called the Y - coordinate of point P. 3). NP is called the Z - coordinate of the point P.
When these three coordinates are taken together, then it is called coordinates of the point P.

A detailed unit conversion table in Hindi.

CENTIMETRE GRAM SECOND SYSTEM (CGS)1). MEASUREMENT OF LENGTH (लंबाई के माप) 10 millimeter = 1 centimetres10 centimetre = 1 decimetres  10 decimetre = 1 metres 10 metre = 1 decametres 10 decametres = 1 hectometres 10 hectometres = 1 kilometres 10 kilometres = 1 miriametresMEASUREMENTS OF AREAS ( क्षेत्रफल की माप )  100 millimetre sq. = 1 centimetre sq.
 100 centimetre sq. = 1 decimetres sq. 100 decimetres sq. = 1 metre sq. 100 metre sq. = 1 decametres sq  100 decametres sq. = 1 hectometres sq. 100 hectometres sq. = 1 kilometres sq. 100 kilometres sq. = 1 miriametres sq.
MEASUREMENTS OF VOLUME ( आयतन की माप) 1000 millimetre cube. = 1 centimetre cube.
 1000 centimetre cube. = 1 decimetres cube. 1000 decimetres cube. = 1 metre cube. 1000 metre cube. = 1 decametres cube. 1000 decametres cube. = 1 hectometres cube. 1000 hectometres cube. = 1 kilometres cube. 1000 kilometres cube. = 1 miriametres cube.
MEASUREMENTS OF VOLUME OF LIQUIDS  (द्रव्य के आयतन का माप) 10 millilitre=…

THE GENERAL THEORY OF RELATIVITY | A Unique way to explain gravitational phenomenon.

Today we are going to talk about a very important and revolutionary concept that is THE GENERAL THEORY OF RELATIVITY.
This theory came into existence after 10 years of special theory of relativity (1905), and published by Albert Einstein in 1915.
This theory generalise the special theory of relativity and refines the Newton's laws of universal gravitation.
After coming this theory people's perspective about space and time has been changed completely. And this theory give a new vision to understand the spacetime geometry.
This theory gives a unified description of gravity as a geometrical properties of space and time.
This theory helps us to explain some cosmological phenomenon that is ,

* why small planets revolve around the big stars?
* Why everything in this universe is keep moving?
* Why mostly planets and stars are spherical in shape?
* Why does gravity create?
* Why does time become slow near the higher gravitating mass. Ie. Gravitational time dilation.
And gravitational…