Given below are the Class 9 ScienceExtra questions and Important Questions for Gravitation
a. Multiple choice questions
b. Very Short answer type
c. Short answer type
d. Long answer type
Multiple choice Questions
Question 1.
Which of the following is true?
a. The acceleration due to gravity acting on a freely falling body is directly proportional to the mass of the body
b. Mass of the object is same on Moon and Earth
c. G value is always constant
d. The weight of an object at the center of earth will be zero
Question 2.
A big stone and small are dropped from the roof of the house at the same time. Which one will reach the ground first?
a. Big Stone
b. Small stone
c. Both at the same time
d. Not able to determine with the given data
Question 3.
The value of acceleration due to gravity of earth
a. Same on equator and poles
b. Is the least at equator
c. Is the least on poles
d. Increase from pole to equator
Question 4.
An object is thrown vertically upwards and rises to a height of 10 m. Calculate the velocity with which the object was thrown upwards? Take g=9.8 m/s^{2}
a. 14m/s
b. 16m/s
c. 10m/s
d. 9.8 m/s
Question 5.
The time taken by the object to reach the highest point in the above question
a. 1.42s
b. 1.5 s
c. 1 s
d. 1.43 s
Question 6.
Which of the them is true for two bodies separated by some distance?
a. When the distance between them is halved, Gravitational force becomes 4 times
b. When one of the mass becomes halved, Gravitational force becomes halved
c. When the distance between them is increased four times, Gravitational force becomes 1/16 times
d. None of the above
Question 7. The Weight of the body at a certain place is 30 N. The acceleration due to gravity at that point is 10 m/s^{2}. Find out the mass and weight of the object at the place where acceleration due to gravity is zero?
a. 3 kg ,0 N
b. 3 Kg,30 N
c. 3 Kg,3 N
d. None of these
Question 8. The acceleration due to gravity at three point A,B and C are 9.8 m/s^{2} ,10m/s^{2} and 5 m/s^{2} on the earth surface?
Which of the following is true?
a. B is at least distance out of three point from the center of the earth
b. C is at farthest distance out of three point from the center of the earthv
c. Weight of the object is lowest at point C out of three point
d. The weight of the object varies as
$W_B > W_A > W_C$
Answer
1 (b), (d), (c) 2 (c) 3 (c) 4
Distance traveled, s = 10 m
Final velocity, v = 0 m/s
Acceleration due to gravity, g = 9.8 m s^{2}
Acceleration of the object, a = -9.8 m s^{2}
$v^2= u^2+ 2as$
$0 = u^2+ 2 \times (-9.8) \times 10$
$u^2= 2 \times 9.8 \times 10$
u = 14 m/s
5
$v = u + a t$
$0 = 14 - 9.8 \times t$
t = 1.43 s.
6 (a) (b) (c)
The above can be simply calculated from the below formula
$F=\frac{Gm_{1}m_{2}}{r^{2}}$ 7:
Mass of the body=$ \frac {30}{10}=3 Kg$
Since Mass remains same everywhere, Weight varies as per acceleration due to gravity which is zero at g=0
Hence (a) 8 :All are correct and self explanatory
Very Short Questions
Question 9.
What is the difference between mass and Weight? Question 10.
Derive the inverse square of Newton. Question 11.
Define ‘G’ and give its value. Question 12.
State Archimedes principle?
Answer
It states that when an body is fully or partially immersed in a fluid, it experiences an upthrust, which is equal to the weight of water displaced by the immersed portion of the body
Question 13.
In what direction does the buoyant force on an object immersed in a liquid act?
Answer
Upward direction
Question 14. Is acceleration due to gravity (g) constant?. Tell us how it is there at different places on earth?
What are these:
(i) Product Rule
(ii) Inverse Square rule
(iii) Universal gravitational constant
(iv) Universal law of gravitation
Answer
acceleration due to gravity (g) is not constant. It varies with different planet and it is different at different places on earth. It varies as per Inverse Square rule
Short Answer type
Question 15. A ball is thrown up with speed of 10 m/s. How high will it go before it begins to falls? Take g=10m/s^{2}
Answer
v=0 ,u=10m/s a=-10m/s^{2}, h=?
$v^2=u^2 +2ah$
Substituting the above values
H=5 m
Question 16.
The weight of the man on earth is 150 N and on certain planet is 25 N.
Take g=10m/s^{2} on earth
a.Find the mass of the man on earth and planet
b. Find the acceleration due to gravity on the planet
Answer
Weight on earth =150 N
So, mass of man on earth= $ \frac {150}{10}=15 kg$.
Now mass does not varies and it will remain same on earth and planet
Now weight on Planet=25N
Now as mass =15 kg
Acceleration due to gravity on Planet= $ \frac {25}{15}=1.66$ m/s^{2}
Question 17.
The pressure exerted by a cube of side 0.03m on a surface is 10Pa. Calculate the thrust exerted by the cube?
Question 18.
The mass of a block made of certain material is 13.5 kg and its volume is $15 \times 10^{-3} m^3$. Will the block float or sink in water?
Answer
$Density = \frac {mass}{volume}$
$Density = \frac {13.5}{15 \times 10^{-3} }=900 kg/m^3$
Now density of water is 1000kg/m^{3}. So block density is less than that of water. Hence block will float
Question 19.
Why does a body lose weight when immersed in a liquid?
Answer
When a body is immersed in liquid, an upward force acts on the body which is equal to the weight of water displaced by the immersed portion of the body. So net gravtational force becomes less and body lose weight
Question 20.
State the conditions under which a body will sink or float in a fluid?
Answer
a. if the density of the body is higher than the density of liquid,then it would sink.
b. if the density of body is less than the density of liquid,then it would float.
Question 21.
Mona weighs 750 N on earth.
(i) What will be Mona�s mass on Earth ($g = 10 \ ms^{-2}$)
(ii) On the planet Mars, the force of gravity is 38% of that of Earth. How much will Mona weigh on Mars? Question 22.
The ratio of the gravitational force on Neptune to the gravitational force on earth is 9 : 8. Ramesh weighs 792 N on earth. Calculate his weight on Neptune. Question 23.
If a fresh egg is put into a beaker filled with water, it sinks. On dissolving a lot of salt in the water, the egg begins to rise and then floats. Why?
Answer
The salt solution has much more density then the plain water solution.Now the density of salt solution is more than egg,so egg begins to float
Question 24.
Give three points of differences between mass and weight. Question 25.
If the earth attracts an apple, does the apple also attract the earth? If so, why does the earth not move towards the apple?
Long answer type
Question 26.
(i)Define pressure?
(ii)Give its mathematical expression and its SI unit?
Answer
The thrust on unit area is called pressure.
$Pressure = \frac {thrust}{Surface \; Area}$
Its SI unit is Pascal
Question 27.
(i)State the mathematical formula that relates thrust and pressure.
(ii) List the factors on which the pressure depends and explain how it depends on them? Question 28.
Differentiate between thrust and pressure? Question 29.
Differentiate between density and relative density?
Answer
Density: Mass per unit volume of a substance is called density. SI unit is kg/m^{3}
$ density= \frac {mass}{volume}$
Relative Density: The ratio between density of a substance and density of water is called relative density.Relative density has no units because it is the ratio between the similar physical quantities
$Relative \; density = \frac {density \; of \; the object}{density \; of \; water}$
Question 30. Define buoyancy. State the factors on which buoyant force depends?
Answer
Buoyancy is the upward force acting on the body when it is submerged in a liquid
buoyant force Depends on
a.Volume of the fluid displaced.
b.Density of the fluid in which the body is immersed.
c. Acceleration due to gravity at the place.
Question 31. Give reasons
(i)How do snow shoes stop you from sinking into snow?
(ii)Explain the force responsible for the following:
(a) Moon revolves around the earth.
(b) Objects lying apart on earth attract each other, yet they do not cling to each other.
Answer
(i)Snow shoes are very large and have large surface area.Since the surface area is large than the pressure exerted by the shoes will be less on ground. So due to this person will not sink into snow.
(ii) Gravitational force
Question 32
Answer the following questions:
(a) State the type of motion shown by a freely falling stone.
(b) When a stone is thrown vertically upwards, its velocity is continuously decreased. Why?
(c) Give an example of a motion in which average velocity is zero, but the average speed is not zero. Question 33
Explain with Reason
(a) On moon, man feels lighter than earth.
(b) Mass is scalar while weight is a vector quantity.
(c) What is meant by Free fall
(d) what is Acceleration due to gravity?
Summary
This gravitation class 9 important questions and answers is prepared keeping in mind the latest syllabus of CBSE . This has been designed in a way to improve the academic performance of the students. If you find mistakes , please do provide the feedback on the mail.