Students can Download Science Chapter 10 Gravitation Questions and Answers, Notes Pdf, KSEEB Solutions for Class 9 Science helps you to revise the complete Karnataka State Board Syllabus and to clear all their doubts, score well in final exams.

## Karnataka State Syllabus Class 9 Science Chapter 10 Gravitation

### KSEEB Class 9 Science Gravitation Intext Questions and Answers

Question 1.

State the universal law of gravitation.

Answer :

Every’ object in the universe attracts every other object with a force that is proportional to the product of their masses and inversely proportional to the square of the distance between them.

∴ \(\mathrm{F}=\frac{\mathrm{GMm}}{\mathrm{d}^{2}}\)

Question 2.

Write the formula to find the magnitude of the gravitational force between the earth and an object on the surface of the earth.

Answer :

\(g=G \frac{M}{d^{2}}\)

Question 3.

What do you mean by free fall?

Answer :

Objects fall towards the earth under the gravitational force influence, then we say that objects are in free fall.

Question 4.

What do you mean by the acceleration due to gravity?

Answer :

The force with which the body attracted towards the earth is called acceleration due to gravity, it is denoted by ‘g’.

Question 5.

What is the difference between the mass of an object and its weight?

Answer :

Mass: Total matter contained in a body, scalar quantity. Weight: Depends upon the mass of a body, vector quantity.

Question 6.

Why is the weight of an object on the moon is \(\frac{1}{6} \text { th }\) its weight on the earth?

Answer :

Mass of the moon is less than the moon of earth

Question 7.

Why is it difficult to hold a school bag having a strap made of a then and strong string.

Answer :

The force depends upon Area, in thin strap thickness is less influences more pressure.

Question 8.

What do you mean by buoyancy?

Answer :

The property of liquid exerts an upward force to push the objects towards the surface.

The buoyant force depends upon the density of the liquids.

Question 9.

Why does an object float or sink when placed on the surface of the water?

Answer :

If the objects of density less than that of a liquid float on the liquid. The objects of density greater than that of a liquid sink in the liquid.

Question 10.

You find your mass to be 42 kg on a weighing machine is your mass more or less than 42 kg?

Answer:

W α m x g x h – h = 1

W = m x g x h – g = 10

Weight is depending upon the mass of an object.

∴ it is more than 42 kg.

Question 11.

You have a bag of cotton and iron bar each indicating a mass of 100 kg when measured on a weighing machine in relating one is heavier than others. Can you say which one is heavier and why?

Answer :

Iron bar is heavier as its density is more than that of cotton.

### KSEEB Class 9 Science Gravitation Textbook Exercise Questions and Answers

Question 1.

How does the force of gravitation between two objects change when the distance between them is reduced to half?

Answer :

Force is increased by four times.

Question 2.

Gravitational force acts on all objects in proportion to their masses. Why then, a heavy object does not fall faster than a light object?

Answer :

The gravity of heavier objects is more than light objects.

Question 3.

What is the magnitude of the gravitational force between the earth and a 1 kg object on its surface? (Mass of the earth is 6 x HP kg and radius of the earth is 6.4 x 10^{6} m)

Answer :

\(\begin{aligned}

\mathrm{g}=\mathrm{G} \frac{\mathrm{M}}{\mathrm{R}^{2}} &=\frac{6 \times 10^{24}}{6 \cdot 4 \times 10^{6}} \times 6 \cdot 026 \times 10^{-11} \\

&=9.8 \mathrm{N}

\end{aligned}\)

Question 4.

The earth and the moon are attracted to each other by gravitational force. Does the earth attract the moon with a force that is greater or smaller or the same as the force with which the moon attracts the earth? Why?

Answer :

Mass of earth is more than that of the moon. Therefore the earth attracts the moon more than that of the moon attracts the earth.

Question 5.

If the moon attracts the earth, why does the earth not move towards the moon?

Answer :

Earth has more weight which is 6 times larger than that of the weight of the moon.

Question 6.

What happens to the force between two objects? if

(i) the mass of one object is doubled?

Answer :

doubled (increases)

(ii) the distance between the

objects is doubled and

Answer :

\(\frac{1}{4}\) times ; friplcd \(\frac{1}{(3)^{2}}=\frac{1}{9}\) times

(iii) the masses of both objects are doubled?

Answer :

Increases by 4 times

Question 7.

What is the importance of the universal law of gravitation?

Answer :

(a) Mass of an object can -be determined.

(b) Distance between the objects can be determined.

(c) The motion of the moon around the easier.

Question 8.

What is the acceleration of free fall?

Answer :

The body changes its velocity in -unit time during its free fall.

g = 9.8 m 1s^{2}

Question 9.

What do we call the gravitational force between the earth and an object?

Answer :

Acceleration due to gravity. (Gravitational force)

Question 10.

Amit buys few grams of gold at the poles as per the instruction of one of his friends. He hands over the same when he meets him at the equator. Will the friend agree with the weight of gold bought? If not, why?

Hint: The value of g is greater at the poles than at the equator.

Answer :

Weight differs from poles to the equator.

W = m x g ploes W_{p} = m x g

W α m Equator W_{e} = m x g

W α g Weight of gold at the equator is less than weight at poles

Question 11.

Why does a sheet of paper fail slower than one that is crumpled into a ball?

Answer :

The surface area is more reduces due to sinking air resistance.

Question 12.

The gravitational force on the surface of the moon is only \(\frac{1}{6}\) as strong as gravitational force on the earth. What is the weight in newtons of a 10 kg object on the moon and on the earth?

Answer :

Earth as Moon

W = m x g = 10 x 9.8 = 98N

Weiaht on moon = \(\frac{98}{6}\) =16.3 N.

Question 13.

A ball is thrown vertically upwards with a velocity of 49 m/s. Calculate (i) the maximum height to which it rises (ii) the total time it takes to return to the surface of the carthi

Answer :

(a) V^{2 }– u^{2 }= 2gs

0^{2} – (9.8)^{2} = 2 x (-9.8) x 5

S = 122.5 M

(b) V = u + at 0

= 49 + (- 9.8)f

t = 5 sec

Total time = 5 + 5 = 10 sec

Question 14.

A stone is released from the top of a tower of height 19.6 m. Calculate its final velocity just before touching the ground.

Answer :

u = 0 m/s ; h=s = 19.6 m

g = 9 8 m/s^{2}

V^{2} – u^{2} = 2gs

V^{2 }– 0^{2 }= 2 x 9 x 8 x 19.6

V^{2} = 19.6 x 19.6

∴ V = 19.6 m/s

Question 15.

A stone is thrown vertically upward with an initial velocity of 40 m/s. Taking g = 10 m/s^{2}, find the maximum height reached by the stone. What are the net displacement and the total distance covered by the stone?

Answer :

h = s ; v^{2 }– u^{2 }= 2gs

0^{2} – (40)^{2} = 2 x (-10)s

∴ s = 80 m

Tola! distance = 80m + 80m = 160 m

Question 16.

Calculate the force of gravitation between the earth and the Sun, given that the mass of the earth = 6 x 10^{24} kg and of the Sun = 2 x 10^{30} kg. The average distance between the two is 1.5 x 10^{11} m.

Answer :

= 6 x 10^{24} kgM_{s} = 2 x 10^{30} kg

d = 1.5 x 10^{11
}

Question 17.

A stone is allowed to fall from the top of a tower 100 in high and at the same time, another stone is projected vertically upwards from the ground with a velocity of 25 m/s. Calculate when and where the two stones will meet.

Answer :

Question 18.

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.

Answer :

(a) u = 0, v = 0, g = -9-8 m/s^{2}

Total time taken

= 6 sec (up + down)

Time for upward journey = \(\frac{6}{2}\) = 3s

v = u + gt

0 = u + (-9.8) x 3

u = 29.4 m/s

(b) Maximum height

S = ut + \(\frac{1}{2}\) gt^{2}

= (29.4 x 3) + \(\frac{1}{2}\) (- 9.8) (3)^{2}

h = 44.1 M

(c) Position after 4 sec

s = ut + \(\frac{1}{2}\) gt^{2}

s = (29.4 x 4) + \(\frac{1}{2}\) (-9.8) x 4^{2}

=117.6 – 78.4 = 39.2 M.

Question 19.

In what direction does the buoyant force on an object immersed in a liquid act?

Answer :

Opposite to the direction of immersion.

Question 20.

Why does a block of plastic released under water come up to the surface of the water?

Answer :

Density of the block of plastic less than that of water (Buoyant force)

Question 21.

The volume of 50 g of a substance . is 20 cm^{3}. If the density of water is 1 g enr^{-3}, will the substance float or sink?

Answer :

\(\mathrm{d}=\frac{\mathrm{M}}{\mathrm{V}}=\frac{50}{20}=2 \cdot 5 \mathrm{g} / \mathrm{cm}^{2}\)

Density of substance more than the density of water. The substance will sink of water.

Question 22.

The volume of a 500 g sealed packet is 350 cm^{3}. Will the packet float or sink in water if the density of water is l g cm^{-3}? What will be the mass of the water displaced by this packet?

Answer :

m = 500 gm. V = 350 cm^{3}

Mass = Volume of pocket x density = 350 x 1 = 350 g

\(d=\frac{m}{v}=\frac{50 \not p}{35 p}=\frac{10}{7}=1.428 \mathrm{g} / \mathrm{cm}^{3}\)

Packets sinks because its density is more than water.

Question 23.

A car falls off a ledge and drops to the ground in 0.5 s. Let g = 10 ms^{-2 }(for simplifying the calculations).

(i) What is its speed on striking the ground?

(ii) What is its average speed during the 0.5 s?

(iii) How high is the ledge from the ground?

Answer :

Time, t = \(\frac{1}{2}\) second

Initial velocity, u = 0 m s^{-1}

Acceleration due to gravity, g = 10 m s^{-2}

Acceleration of the car, a = + 10 m s^{-2} (downward)

(i) speed v = at

v = 10 ms^{-2} x 0.5 s = 5 ms^{-1}

(ii) average speed

\(\begin{aligned}

&=\frac{u+v}{2}\\

&=\frac{\left(0 \mathrm{ms}^{-1}+5 \mathrm{ms}^{-1}\right)}{2}

\end{aligned}\)

(iii) distance travelled,

\(\begin{aligned}

\mathrm{s} &=\frac{1}{2} \mathrm{at}^{2}=\frac{1}{2} \times 10 \mathrm{ms}^{-2} \times(0 \cdot 5 \mathrm{s})^{2} \\

&=\frac{1}{2} \times 10 \mathrm{ms}^{-2} \times 0 \cdot 25 \mathrm{s}^{2}=1.25 \mathrm{m}

\end{aligned}\)

Thus,

(i) its speed on striking the ground

= 5 m s^{-1}

(ii) its average speed during the 0.5 s

= 2.5 ms^{-1}

(iii) height of the ledge from the ground

= 1.25 m.

24. An object is thrown vertically upwards and rises to a height of 10 m. Calculate (i) the velocity with which the object was thrown upwards and (ii) the time taken by the object to reach the highest point.

Answer :

Distance travelled, s = 10 m

Final velocity, v = 0 ms^{-1}

Acceleration due to gravity, g = 9.8 ms^{-2}

Acceleration of the object,

a = – 9.8 m s^{-2} (upward motion)

(i) v^{2} = u^{2} + 2as .

0 = u^{2} + 2 x (-9.8 ms^{-2}) x 10 m

– u^{2} = – 2 x 9.8 x io m^{2}s^{2}

u = \(\sqrt{196}\) ms^{-1}

u = 14 m s^{-1}

(ii) v = u + at

0 = 14 ms^{-1} – 9.8 ms^{-2} x t

t = 1.43 s.

Thus,

(i) Initial velocity, u = 14 m s^{-1}, and .

(ii) Time taken, t = 1.43 s.

### KSEEB Class 9 Science Gravitation Additional Questions and Answers

Question 1.

Why is Newton’s law of Gravitation called universal law?

Answer :

It is applicable to all bodies either they ‘ are small or big. Whether they are celestial or terrestrial.

Question 2.

What is the density of water at 4°C?

Answer :

Density of water at 4G = 1000 kg/m3.

Question 3.

Mention two factors on which the buoyant force acting on an object depends?

Answer :

(i) The volume of the object, immersed in the liquid.

(ii) The density of the fluid in which the object is immersed,

Question 4.

An egg sinks in freshwater but floats in highly salty water. Give reason.

Answer :

Upthrust acting on the egg in freshwater in less than the weight of the egg, therefore, it sinks in freshwater. However, the density of salty water is much greater than the density of freshwater. So upthrust acting on the egg in salty water is greater than the weight of the egg.

Question 5.

Why are big boulders can be moved easily by floods?

Answer :

Big boulders weigh less while in water and as such as easily moved by floods.