# Gravitation Numericals with Solutions for Class 9

Given below are the class 9 physics gravitation Numericals .It includes thrust,pressure,relative density numericals along with Archimedes principle numericals
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Question 1.
A solid weighs 200 gf in air, 160 gf in water and 170 gf in a liquid. Calculate the relative density of the solid and that of the liquid?

Question 2.
Define thrust. A force of 150N acts on a surface of area $15 \; cm^2$. Calculate thrust and pressure?

Question 9.
Relative density of gold is 19.3. The density of water is $1000 \; kg/m^3$. Find the density of gold in SI unit in g/cc?

Question 3.
The volume of a 350g sealed tin is 200 cubic.cm. Find the density of the tin in g/cc. Also find the density in SI unit?

Question 4.
Relative density of silver is 10.8? What is the density of silver in SI unit?. Given The density of water is $1000 \; kg/m^3$

Question 5.
A force of 250N acts on a surface of area $15cm^2$. Calculate thrust and pressure?

Question 6.
A force of 400N acts on a surface of area 25cm2. Calculate thrust and pressure? Calculate the changed pressure if the force now is made to 600N?

Question 7.
Define relative density. Relative density of mercury is 13.6. The density of water is 1000 kg/m3. What is the density of mercury in SI unit?

Question 8.
You are provide with a hollow iron ball of volume 20cm3, mass of 15g and a solid iron ball of mass 20g. Both are placed on the surface of water contained in a large tub. What will float? Give reason for your answer? Given density of iron= 8 g/cc

Question 9.
The dining has dimensions $50 \;m \times 15 \; m \times 3.5 \; m$. Calculate the mass of air in the hall? (Density of air= 1.30kg/m3)?

Question 10.
Mass of body 'A' is equal to mass of body 'B'. If the density of body 'A' is greater than the density of body 'B', which is easier to lift through air?
Question 11.
A force of 100N acts on a surface of area 25m2? Calculate thrust and pressure. Calculate the changed pressure if the force now is reduced to 25N?

Question 12.
Two objects of masses $m_1$ and $m_2$ having the same size are dropped simultaneously from heights $h_1$ and $h_2$ respectively. Find out the ratio of time they would take in reaching the ground. Will this ratio remain the same if
(i) one of the objects is hollow and the other one is solid
(ii) both of them are hollow, size remaining the same in each case. Give reason?

Question 13.
A piece of iron weighs 44.5gf in air, 39.5 gf in water and 40.3 gf in an oil. Find:
a.the relative density of iron.
b. the density of oil in SI unit. What assumption have you made in your calculation?
Given density of water=1 gm/cc = 1000 kg/cubic m

Question 14.
A solid weighs 50 gf in air(where gf is gram force) and 44 gf when completely immersed in water. Calculate:
a.the upthrust
b.the volume of the solid
c. the relative density of the solid
Given Density of water=$1000 kg/m^3$

Question 15.
An ball is thrown vertically upwards and rises to a height of 10 m.
Calculate
(i) the velocity with which the object was thrown upwards
(ii) the time taken by the object to reach the highest point.?

Question 16.
A block of wood of mass 10kg and dimensions $40 \; cm \times 25 \;cm \times 10 \;cm$ is placed on a table top. Find the pressure exerted if the block lies on the table top with sides of dimension:
a.$10 \; cm \times 25 \; cm$
b.$40 \; cm \times 10 \; cm$

Question 17.
Find the ratio of the pressure exerted by a block of 400N when placed on a table top along its two different sides with dimensions $20 \; cm \times 10 \; cm$ and $10 \; cm \times 15 \; cm$.

Question 18.
If two forces in the ratio 5:7 act on two areas in the ratio 4:5, Find the ratio of pressure exerted?

Question 19.
The mass of the earth is $6 \times 10^{24} kg$ and that of the moon is $7.4 \times 10^{22} kg$. If the distance between the earth and the moon is $3.84 \times 10^{5} km$,calculate the force exerted by the earth on the moon. $G = 6.7 \times 10^{-11} N m^2 kg^{-2}$.?

Question 20.
Acceleration due to gravity at Height H above earth surface is half of the value of Acceleration due to gravity at the surface. What is the value H in terms of R where R is radius of Earth

Question 21.
A ball is dropped from a height of 20 m. a second ball is thrown downwards from the same height after one second with initial velocity u. if both the balls reach the ground at the same time, calculate the initial velocity of the second ball. (Take $g = 10 \ ms^{-2}$)
Question 22. What happens to the gravitational force between two objects if:
(i)The mass of one object is doubled?
(ii)The distance between the objects is doubled?
(iii)The masses of both the objects are doubled?
(iv)The distance between them is halved?
(v)Mass of one of the objects is halved?
(vi)the distance between them is reduced to $\frac{1}{4}$th

Question 23. Find the gravitational force between the sun and the earth. The mass of the sun is $2.0 \times 10^{30}$ kg, and the mass of the earth is $6.0 \times 10^{24}$ kg. the distance between the sun and the earth is 1.5 \times 1011 m. ($G = 6.67 \times\ {10}^{-11}\ {Nm}^2\ {kg}^{-2}$).
Question 24
A ball thrown vertically up returns to the thrower after 6 s. find:
(i) The velocity with which it was thrown up.
(ii) The maximum height it reaches.
(iii) Its position after 4 s.
Question 25
At what height above the earth’s surface would the value of acceleration due to gravity be half of what is on the surface? Calculate.
Question 26
Communication satellites move in orbits of radius 44,400 km around the earth. Find the acceleration of such a satellite assuming that the only force acting on it is that due to the earth. Mass of the earth = $6 \times\ {10}^{24}$ kg. (G = $6.67 \times\ {10}^{-11}\ {Nm}^2\ {kg}^{-2}$).

Question 27
Find the weight of an object at the height 6400 km above the earth’s surface. The weight of the object at the surface of the earth is 20 N and the radius of the earth is 6400 km.
Question 28
A fire cracker is fired and it rises to a height of 1000 m. find the
(i) velocity by which it was released.
(ii) time taken by it to reach the highest point (take $g = 10 \ ms^{-2}$)
Question 29
A car falls off a ledge and drops to the ground in 0.5 s. let $g = 10 \ ms^{-2}$.
(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 edge from the ground?

Question 30
The value of 'g' on earth’s surface is $9.8 \ m/s^2$. Suppose the earth suddenly shrinks to one – third of its present size without losing any mass. What is the value of g on the surface of shrinked earth?

## Summary

This gravitation class 9 numericals with solutions 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.