Question:
What do you mean by Thrust or Buoyant force?
Answer:
The upward force exerted by a liquid when a body is immersed in the liquid is called thrust or Buoyant Force.
Note: When in equilibrium the buoyant force is balanced by the weight of an object or the force of gravity acting on it.
Gravitation
Q 1.
What is the SI unit of weight ?
Q 2.
Fill in the blanks :
The value of
g ________ (increases/decreases) as we go upwards from the earth's surface.
Q 3.
What is the source of centripetal force that a planet requires to revolve around the Sun ? On what factors does that force depend ?
Q 4.
What is the SI unit of mass ?
Q 5.
State Kepler’s Laws of planetary motion.
Q 6.
The following figure shows four containers containing a liquid at the same height. Rank them according to the pressure exerted by the liquid on the bottom of the containers in ascending order.
a. 1, 2, 3, 4 b. 4. 3, 1, 2 c. 3, 4, 1, 2 d. same pressure in each case.
Q 7.
Two bodies A and B having masses 2 kg and 4 kg respectively are separated by 2 m.Where should a body of mass 1 kg be placed so that the gravitational force on this body due to bodies A and B is zero ?
Q 8.
A ball is thrown up with a speed of 15 m/s.How high will it go before it begins to fall ? Take g=
Q 9.
What are the differences between the mass of an object and its weight ?
Q 10.
A stone is thrown vertically upward with an initial velocity of 40 m/s.Taking g =
,find the maximum height reached by the stone.What is the net displacement and the total distance covered by the stone ?
Q 11.
Does gravitational force between two objects depend on medium between them ?
Q 12.
Why don’t two objects move towards each other due to gravitational pull between them ?
Q 13.
Can you calculate mass of Earth from Newton’s law of gravitation ?
Q 14.
Whenever a body is thrown up with a certain velocity,the upward motion is opposed by gravitational pull of earth and also by the resistance of air.
Therefore, velocity of the body goes on decreasing. When this velocity becomes zero,the body cannot rise further.It has attained,what is called ‘maximum height’.From this height,the body begins to fall downwards under the action of gravity.
Read the above passage and answer the following questions:
(i) At the highest point,what are the velocity and acceleration of the body?
(ii) What is the maximum height attained by a body thrown upwards with a velocity of 19.6 m/s ? Take g =
.
(iii) What values in life do you learn from this concept ?
Q 16.
The mass of Sun is
kg and mass of Earth is
kg. If the distance between the centres of Sun and Earth is
km,calculate the force of gravitation between them.
Q 17.
What do you mean by free fall ?
Q 18.
How does the force of gravitation between two objects change when the distance between them is reduced to half ?
Q 19.
What is the value of G (i) on Earth (ii) on Moon ?
Q 20.
Which force accelerates a body in free fall ?
Q 21.
What is the usual shape of orbits of planets around the Sun ?
Q 22.
What is value of ‘g’ on Earth ?
Q 23.
How are gravitation and gravity related ?
Q 24.
Write down the equations of motion of objects under the influence of gravitational force of Earth.Explain the meaning of the symbols used.
Q 25.
A physics teacher explains to his students in class,the subject of motion under gravity.When a body is projected upwards from the ground with a certain velocity a,the velocity goes on decreasing at a constant rate due to gravitational pull of earth.At a certain height,this velocity becomes zero.The body cannot rise further.From this maximum height,the body begins to fall and its velocity goes on increasing at the same constant rate due to gravitational pull of earth.The body would strike the ground with exactly the same velocity (v = u),with which it was thrown initially. This is on the assumption that resistance due to air is zero, either way.
Read the above passage and answer the following questions:
(i) Why is velocity of body on striking the ground the same as initial velocity of projection of the body ?
(ii) Does the body take same time to fail to ground as the time it takes to reach the maximum height ?
(iii) What values of life do you learn from this brief study ?
Q 26.
Fill in the blanks :
The value of G was found out by _______ by using a ________.
Q 27.
The tangential velocity of a planet or moon moving in a circle is at a right angle to ____________. (fill in the blank)
Q 28.
Fill in the blanks :
The SI unit of weight is _______.
Q 29.
To estimate the height of a bridge over a river,a stone is dropped freely on the river from the bridge.The stone takes 2 s to touch the water surface in the river.Calculate the height of the bridge from the water level.Take g = 9.8
.
Q 30.
Write the formula to find the magnitude of the gravitational force between the Earth and an object on the surface of the Earth.
Q 31.
What is the acceleration of free fall ?
Q 32.
Does Newton’s third law of motion apply to gravitational force ?
Q 33.
Then why Is the Earth not seen moving towards the stone ?
Q 34.
Can a body have weight but no mass ?
Q 35.
A body weighs 10 kg on the surface of earth.What would be its mass and weight at the centre of earth ?
Q 36.
State and explain universal law of gravitation.What is its importance ?
Q 37.
Define g and G.Establish relation between them.
Q 38.
Why is G called the Universal Constant?
Q 39.
Gravitational force acts on all objects in proportion to their masses. Why then, a heavy object does not fall faster than a light object?
Q 40.
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 earth.
Q 41.
Fill in the blanks :
A body is said to be in _______ when only gravity acts on it.
Q 42.
If the distance of Earth from the Sun were half the present value,how many days will make one year ?
Q 43.
Which force revolves Moon around Earth ?
Q 44.
Who gave three laws of planetary motion ?
Q 45.
Does value of ‘g’ vary from place to place on Earth ?
Q 46.
What is the weight of a body of mass 1 kg on Earth ?
Q 47.
Distinguish between mass and weight.
Q 48.
Fill in the blanks :
The mass of the earth is ________ kg.
Q 49.
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 whichthe moon attracts the earth? Why?
