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Syllabus

what is the difference between density and relative density ?Why Newton's law of gravitation called universal law

How does a lactometer work ?

WHEN A PLANET MOVES AROUND THE SUN, ITS

(A) AREAL VELOCITY IS CONSTANT

(B) LINEAR VELOCITY IS CONSTANT

(C) ANGULAR VELOCITY IS CONSTANT

(D) ALL THE VELOCITIES ARE CONSTANT

what are the importance of universal law of gravitation??

the density of ice is 0.9 g/cm

^{3}. When it floats in water, what fraction of its volume will remain above surface?List two factors on which buoyant force depends.

A sharp knife is more effective than a blunt knife.why?

what happens to the gravitational force between two objects if

i) the mass of one object is doubled

ii) distance between two objects is doubled

iii) masses of both the objects are doubled

what is the difference between density and relative density of a substance

Q. The water level in the measuring cylinder before and after immersing a metal cube is shown in the figure. Calculate the volume of the metal cube.

Why do objects float or sink when placed on the surface of liquid?

what is the relationship between "G" and "g"?

(a) is same on equator and poles

(b) is least on poles

(c) is least on equator

(d) increases from pole to equator

Difference between thrust and pressure?

During Freefall, what is the weight of a body? Give reason for your answer.

A ball thrown up vertically returns to the thrower after 6 s. Find

(a) the velocity with which it was thrown up,

(b) the maximum height it reaches, and

(c) its position after 4 s.

why do we use constant e.g. K, G etc., to remove proportional sign from the equations?

A solid weighs 80g in air and 64g in water. Calculate its relative density. Also tell, when kept in water would the object float or sink.

why is it difficult to hold a school bag having a strap made of thin & strong strip?

What happens to the force between two objects, if

(i) the mass of one object is doubled?

(ii) the distance between the objects is doubled and tripled?

(iii) the masses of both objects are doubled?

Guys, it's urgent, plz answer them immediately...

Q1. A block weighing 1.0 kg is in the shape of a cube of length 10 cm. It is kept on a horizontal table. Find the pressure on the portion of the table where the block is kept. (ans. 1000Pa)

^{2}and atmospheric pressure (1atm) =1.013×10^{5}Pa.^{}(ans.15.2 ton wt)Q3. Calculate the mass of a body whose volume is 2 m

^{3}and density 0.52 g/cm^{3}. (ans. 1040 kg)Q4. A dining hall has dimensions 50m× 15m × 3.5m. Calculate the mass of air in the hall. Given, density of air =1.30kg/m

^{3}. (ans. 3412.5 kg)Q5. A thread of mercury of 10.2 g is in a tube of uniform cross section 0.1cm

^{3}. Calculate the length of thread. The density of mercury is 13.6g/cm^{3}. (ans. 7.5cm)Q6. A cubical block of water is dipped completely in water. Each edge of the block is 1cm in length. Find the buoyant force acting on the block. (ans. 10

^{-2}N)Q7. A body of mass 2.0 kg and density 8000 kg/m

^{3}is completely dipped in a liquid of density 800 kg/m^{3}. Find the force of buoyancy on it. (ans. 2N)Q8. A piece of iron of density 7.8 × 10

^{3}kg/m^{3}and volume 100 cm^{3}is totally immersed in water. Calculate (a) the weight of the iron piece in air (b) the upthrust and (c) apparent weight in water. (ans. (a) 7.8N (b) 1N (c) 6.8 N)Q9. A solid body of mass 150g and volume 250cm

^{3}is put in water. Will the body float or sink.Q10. A solid of density 5000kg/m

^{3}weights 0.5 kg in air. It is completely immersed in water of density 1000kg/m^{3}.^{3}? (ans. 0)Q11. The mass of a block made of certain material is 13.5 kg and its volume is 15 × 10

^{-3}m^{3}. Will the block float or sink in water. Give reason for your answer.Q12. (a) What is the density of air in NTP? (b)What is the unit of relative density?

Q13. (a) When does a body sinks in a fluid?

(b)Why does a balloon filled with hydrogen gas rise up against gravity?

Q15. (a). A body weighs 10 N in air and 8 N when fully immersed in water. How much is the buoyant force acting on the body?

Gravitation - An OverviewThe picture that opens this lesson shows our location in the Milky Way galaxy. We are about 26,000 light years away from the centre of the galaxy. We are residing in this location from the very beginning of the Universe. This shows that there exists a powerful force that holds us in our place since the inception of the Universe. This force binds everything from stars to

galaxiestosuperclustersand is known as theGravitational force.Universal Law of GravitationIt is common to see things falling to the ground. The falling of a body to the ground is attributed to Earths attraction for it. In fact, the weight of a body is expressed in terms of this force of attraction.

Newtons experiments showed that Earths attraction, when at a constant distance from another body, varied directly with the mass of the other body. However, this was only a partial expression of the general law of gravitation. This law states that

every particle of matter attracts every other particle with a force that is directly proportional to the product of their masses and inversely proportional to the square of the distance between them.All planets in the solar system are bound to revolve in their fixed orbits by the gravitational attraction of the sun. The same force of gravity acts between Earth and the moon, making the moon revolve around Earth in its fixed orbit.

Falling of a ball from a heightFalling of raindrops from cloudsRevolution of planets around the sunGravitational Force - Mathematical FormLet two objects

IandII,of massesM_{1}andM_{2}respectively, be placed at a distancedfrom each other. As per the law of gravitation, the following two assertions can be made about the force of gravity (F) between the two objects.(a)The force of gravity between the two objects is directly proportional to the product of their masses. This is expressed as:F∝M_{1}×M_{2}(By Product rule)(b)The force of gravity between the two objects is inversely proportional to the square of the distance between them. This is expressed as:F∝ (1/d^{2})_{}(By Inverse-Square rule)On combining both the equations, we obtain:

F ∝M1M2d2 or F =GM1M2d2 " width="195" height="31" src="http://img1.mnimgs.com/img/study_content/editlive_lp/62/2013_02_09_10_27_23/mathmlequation3568840687176322813_1624553838655146822.png" /

Where, G is a constant called

Universal Gravitational ConstantorNewtons constant.Universal Gravitational ConstantUniversal Gravitational Constant (G) is a constant of proportionality. Its value is constant at all places in the universe. Its value does not depend on the medium between two bodies.

SI unit of GThe force of gravity (

F)between two objects of massesM_{1}andM_{2},_{}which are at a distancedfrom each other, is given as:F = GM1M2d2 or G =Fd2M1M2 " src="http://img1.mnimgs.com/img/study_content/editlive_lp/62/2013_02_09_10_27_23/mathmlequation6404826584263522868.png" /

On substituting the SI units of the various quantities in this equation, we obtain: G = Nm

^{2}/ kg^{2}Therefore, the SI unit of G is Nm^{2}/kg^{2}.Value of GHenry Cavendish found the value of

Universal Gravitational Constant,G with the help of a very sensitive balance. Its value is6.673 × 10^{11}Nm^{2}/kg^{2}Consider two bodies, each having the mass 1 kg. They are placed at a distance 1m from each other. Using the value of G, the force of attraction is given as:

Universal Gravitational ConstantCAN U SIMPLIFY THIS EXPRESSION

Determination of 'G' byHenryCavendishThe value of universal gravitational constant (G) was first determined by Henry Cavendish through the torsion bar experiment. The apparatus of this experiment comprises two pairs of spheres. Each pair of spheres forms a dumbbell having a common axis, as shown in the figure. One of the dumbbells is suspended from a quartz fibre. It rotates freely when the fibre is twisted. The position of a reflected light spot from a mirror attached to the fibre gives the measure of the amount of twists. The second dumbbell can be swivelled in such a way that each of its spheres is close to one of the spheres of the other dumbbell. The gravitational attraction between the two pairs of spheres twists the fibre and the magnitude of the force of gravity is calculated by measuring the amount of twists in the fibre.

The value of G, as determined by Cavendish, came out to be

6.67 × 10^{-11}Nm^{2}/kg^{2}.Universal Law of GravitationGravity in the Earth-Moon SystemUniversal Law of GravitationImportance of the Universal Law of GravitationThe universal law of gravitation helps us understand several natural phenomena. Some of these are given below.

Dropped objects fall toward the ground.Earth pulls all objects toward itself through the gravitational force. Hence, when any object is dropped, it falls toward the ground.

The moon revolves around Earth.The moon is attracted by Earths gravitational force. This keeps the moon revolving around Earth in its orbit of movement.

The planets revolve around the sun.The gravitational attraction between the sun and the planets binds the planets in their respective orbits around the sun.

High and low tides occur on Earths surface.The water present on Earths surface (in oceans, seas, etc.) is attracted by the gravitational forces of the sun and moon. Hence, the level of water in the seas and oceans rises and falls depending on the relative positions of the sun and moon. This causes high and low tides on Earth.

Formation of TidesThe water present on Earths surface (in oceans, seas, etc.) is attracted by the gravitational forces of the sun and moon. Hence, the level of water in the seas and oceans rises and falls depending on the relative positions of the sun and moon. This causes high and low tides on Earth.

Keplers Laws of Planetary Motion

A German astronomer Kepler concluded the orbits of the planets to be circular. the laws which he gave are:

First Law: The orbits of the planets are in the shape ofellipse, having the sun at one focus.In the figure, the sun is not at the centre of the ellipse. It is at one of the foci marked X. The planet follows the ellipse in its orbit. This means that the distance between a planet and the sun constantly changes as the planet revolves in its orbit.

Second Law: The area swept over per hour by the radius joining the sun and the planet is the same in all parts of the planets orbit.In the figure, the imaginary line joining the sun and the planet sweeps out equal areas in equal times. The planet moves faster when it is nearer to the sun. Thus, a planet executes elliptical motion with constantly changing speed as it moves around the sun in its orbit. The point of nearest approach of the planet to the sun is termed perihelion and the point of greatest separation is termed aphelion.

Third Law: The squares of the periodic times of the planets are proportional to the cubes of their mean distances from the sun.It implies that the time taken by a planet to revolve around the sun increases rapidly with the increase in the radius of its orbit.

Keplers Laws of Planetary MotionNewton and the Inverse-Square Rule

Newtons universal law of gravitation states that the force between two bodies is inversely proportional to the square of the distance between them. Hence, this law is also known as the inverse-square rule. Mathematically, this can be expressed as:

F∝ 1/r^{2}...(1)Newton used Keplers third law of planetary motion to arrive at the inverse-square rule. He assumed that the orbits of the planets around the sun are circular, and not elliptical, and so derived the inverse-square rule for gravitational force using the formula for

centripetal force. This is given as:F=mv^{2}/r^{2}...(2) where,mis the mass of the particle,ris the radius of the circular path of the particle andvis the velocity of the particle.Newton used this formula to determine the force acting on a planet revolving around the sun. Since the mass

mof a planet is constant, equation (2) can be written as:F∝v^{2}/r^{}...(3)Now, if the planet takes time

Tto complete one revolution around the sun, then its velocityvis given as:v= 2r/T^{}...(4) where,ris the radius of the circular orbit of the planetor,

v∝r/T...(5) [as the factor 2 is a constant]On squaring both sides of this equation, we get:

v^{2}∝r/^{2}T^{2}...(6)On multiplying and dividing the right-hand side of this relation by

r, we get:v2 ∝r2T2 ×rr or v2 ∝r3T2×1r ...(7) " src="http://img1.mnimgs.com/img/study_content/editlive_lp/62/2013_02_09_10_27_23/mathmlequation8727827952146380765.png" /

According to Keplers third law of planetary motion, the factor r

^{3}/ T^{2}is a constant. Hence, equation (7) becomes:v^{2}∝ 1/r...(8)On using equation (8) in equation (7), we get:

F ∝ 1r ×1r or F ∝1r2 " /

Hence, the gravitational force between the sun and a planet is inversely proportional to the square of the distance between them.

Newton and the Inverse-Square Rule

Example 1:An imaginary planetP, with an orbit of radiusR, completes one revolution around a star in 64 days. Another planetQhas an orbit of radius 4R. How much time will it take to complete one revolution around the same star?Solution:According to Keplers third law of planetary motion:

(1)

Where,is the time period of revolution ofis the radius of the orbit of

P(2)

Where,is the time period of revolution of

Qandis the radius of the orbit ofQOn dividing (1) by (2), we get:

Keplers Laws and the Inverse-Square RuleLets Reviewstarting from Newton's law of gravitation show that the value of "g" decreases as one goes above the earth's surface.

^_^

why a truck or a motorbus has wider tyres

Explain the reason.

An object is dropped from rest at a height of 150 m and simultaneously

another object is dropped from rest at a height 100 m. What is the difference

in their heights after 2 s if both the objects drop with same accelerations?

How does the difference in heights vary with time?

which is greater the attraction of earth for 1 kg iron or the attraction of 1 kg iron for earth(reason pls)

what are the characteristics of gravitational force.......????

relative density of gold is 19.3.if the density of water is 1000kg/m3 ,what is density of gold in si unit?

radius of an iron sphere is 0.21 cm If density of iron is 7.80g/cc calculate mass

difference between mass and weight

WHAT IS THE S.I. UNIT OF UPTHRUST?

what is the difference between thrust and force?

what is the weight of an object of mass 10 kg on moon and on earth? What is the relation between value of 'g' on earth and on moon? (Take value of 'g' on earth to be = 9.8 m s

^{-2})the acceleration due to gravity on a planet is 1.96m/s

^{2}.If it is safe to jump from a height of 3m on the earth, the corresponding height of the planet will be ?A person weighs 110.84N on moon whose acceleration due to gravity is 1/6 of that earth.if the value of 'g' on earth is 9.8m/s-2(ms-2) calculate

a) 'g' on moon

b) mass of person on moon

c) weight of person on earth

2) how does the value of 'g' on the earth is related to the mass of the earth and its radius?derive it?

How archimedes principle is used to determine the purity of gold?

Write the S.I. unit of G. Why is gravitational constant (G) known as universal constant ?

a stone is allowed to fall from the top of a tower 100m high and at the same time another stone is projected vertically upwards frome the ground with a velocity of 25ms-1 . calculate when and where the 2 stones will meet.

The weight of a man is 690N which contains 5.3 x 10

^{-3}m^{3}of blood. Find blood's weight. Take density of blood as kg/m^{3}When an object is immersed into the fluid two forces act on the object in the vertically opposite directions. Name them and also write the factors on which the magnitude of these forces depends on.

A body weighs 63 N on the surface of the earth. What is the gravitational force exerted on it due to the earth at a height equal to half the radius of the earth?

1. Explain why a balloon filled with helium gas rises in air. Why does the balloon rise to a particular height above ground and does not rise further ?

Name two substances whose density cannot be measured.

A cube of copper was found to have a mass of 0.630kg. What are the dimensions of the cube?(The density of copper is 8.94g/cm

^{3}).1) State Archimedes principle?

2) Give two applications of archimedes principle.

A solid weighs 80g in air, 68g in water and 60g in oil. Calculate the relative density of oil and solid.

difference between g and G .

NAME the instrument used to determine the density of liquids in which balance and graduated cylinder are not required. why this instrument is made heavy near the bottom?.....PLA HLP

how is the least count and the zero error of the spring balance is calculated?

name the factors affecting pressure

which force is responsible for the moon revolving around the earth?

State the laws of floatation.

a stone is thrown vertically upward with a speed of 29.4 m/s. find -

1. the time taken by the stone to reach the maximum height.

2. maximum height reached by the body and

3. show that time of ascent is equal to time of descent.

prove that if a body is thrown vertically upwards, the time of ascent is equal to the time of decent.

A balloon filled with hydrogen gas floats in air. Explain this fact with reason.

Q1 Give reasons:

_{1}_{ }and X_{2}contain same number of nuclei . If 6 $\lambda {s}^{-1}$ and 4$\lambda {s}^{-1}$ are the decay constant of X_{1}_{ }and X_{2}_{ }respectively , the ratio of number of nuclei undecayed of X_{1}_{ }to that of X_{2}_{ }will be 1/e after a time(1) $\frac{1}{2\lambda}s$ (2) $\frac{1}{10\lambda}s$ (3) $\frac{1}{5\lambda}s$ (4) $\frac{1}{8\lambda}s$

Define one pascal.

At what height above the earth's surface would the value of acceleration due to gravity be half of what it is on the surface? Calculate.

(a) Becomes two times (b) Becomes half (c) Does not change (d) Becomes four times

12. If the volume of solid body is reduced to half, then its density

(a) Becomes two time (b) Becomes four times (c) Remains the same (d) becomes half

13. Relative density of a substance depends upon

(a) Mass of the substance

(b) Volume of the substance

(c) Shape of the substance

(d) Material of the substance

A piece of iron of density 7.8 * 103kg/m

^{3}and volume 100 cm^{3}is totally immersed in water. Calculate(a) The weight of the iron piece in air

(b) The upthrust

(c) Apparent weight in water

A stone is thrown vertically upward with a velocity 40m/s and is caught back. Taking g=10m/s2.calculate the maximum height reached by the stone

what are the applications of archimedes principle???

THE RATIO OF THE GRAVITATIONAL FORCE ON NEPTUNE TO THE GRAVITATIONAL FORCE ON EARTH IS 9:8. RAMESH WEIGHS 792N ON EARTH. CALCULATE HIS WEIGHT ON NEPTUNE?

write the factor on which pressure depends

^{3}.The density of air is 1.26 Kg/m^{3}.Calculatea) the weight it can lift

b) the acceleration as it rises

RELATIONSHIP BETWEEN SMALL g AND CAPITAL G

how to make model of lactometer on archimedes principle

[b] thrust

[c] pressure

[d] none of these

why does buildings have wide foundations?

prove that if a body is thrown vertically upward , the time of ascent is equal to the time of descent.

For drinks during the day ,Peter has a cup of hot coffee at a temperature of 90 degree celsius and a cup of cold water ,with a minimum temperature of 5 degree celsius .THe cups are of identical type and size and volume of each drink is same .Peter leave the cup sitting in a room of temperature 20 degreee celsius

WHAT ARE THE TEMPERATURE OF COFFEE AND WATER LIKELY TO BE AFTER 10 MINUTES

EXPLAIN WITH REASON PLZ

A sphere of mass 40 kg is attraced by a second sphere of mass 15 kg when their centers are 20 cm apart, with a force of 0.1 milligram weight. Calculate the value of gravitational constant.

The weight of a body in air is 100N. How much will it weigh in water if it displaces 400cm

^{3}of water?loaded test tube placed in pure milk sinks to a certain mark (M). Now some water is mixed with the milk. Will the test tube sink more or less? Explain.

A Piece of ice is placed gently on the surface of water in a glass so that when ice floats, the water comes up to the brim of the glass. what will happen to the level of water when the ice melts? will it overflow? (2) in the above case what will happen if instead of water the glass is filled with (a) with a liquid denser than water. (b) a liquid lighter than water.