# Gravitation Numericals with Solutions for Class9

Given below are the class 9 physics gravitation ,thrust,pressure,relative density numericals along with Archimedes principle numericals
a. Calculation problems

Question 1.
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 2.
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 3.
What do you understand by 1 Pascal and 1 Newton?

Question 4.
Define thrust. A force of 150N acts on a surface of area $15 \; cm^2$. Calculate thrust and pressure?

Question 5.
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?

Question 6.
Define pressure? Give its mathematical expression and its SI unit?

Question 7.
In what direction does the buoyant force on an object immersed in a liquid act?

Question 8.
Differentiate between density and relative density?

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 10.
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) bothof them are hollow, size remaining the same in each case. Give reason?

Question 11.
How do snow shoes stop you from sinking into snow?

Question 12.
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 13.
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 14.
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 15.
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 16.
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 17.
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 18.
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 19.
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 20.
If two forces in the ratio 5:7 act on two areas in the ratio 4:5, Find the ratio of pressure exerted?

Question 21.
Define thrust? Name the factors on which the pressure depends. If a man standing on a sand surface lies down on the sand, how will the pressure exerted on sand by the man be affected in two positions?

Question 22.
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 23.
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 24.
A force of 250N acts on a surface of area $15cm^2$. Calculate thrust and pressure?

Question 25.
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 26.
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 27.
Two objects of Masses $m_1$ and $m_2$ having the same size are dropped simultaneously from heights $h_1$ and $h_2$, rerspectively. 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 to hollow and the other one is solid; and (ii) both of them are hollow, size remaining the same in each case? Give reasons.
Question 28.
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 $g = 10 \ ms^{-2}$)

• Notes
• Assignments

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