Question:
An object is placed at the surface of the earth and is at distance R from the center of the earth. The object weighs 180N. What will be its weight if it is at distance 3R from the center of the earth.
Answer:
20N. [Hint: See logic in Q16-9(i)]
Gravitation
Q 1.
State Kepler’s Laws of planetary motion. How did Newton guess inverse square law ?
Q 2.
A particle is dropped from a tower 180 m high.How long does it take to reach the ground ? What is the velocity when it touches the ground ? Take g =
Q 3.
Calculate the value of acceleration due to gravity on Moon. Given mass of Moon =
kg, radius of Moon = 1740 km
Q 4.
A boy on a clif£ 49 m high drops a stone.One second later,he throws a second stone after the first.They both hit the ground at the same time. With what speed did he throw the second stone ?
Q 5.
Why do sewing needles and all pins have a sharp pointed tip?
Q 6.
Which force is responsible for tides in the ocean at night ?
Q 7.
Fill in the blanks :
Every object in the universe ________ other bodies.
Q 8.
What is the value of ‘g’ at the centre of Earth ?
Q 9.
What do you mean by acceleration due to gravity ?
Q 10.
Two stones A and B are dropped from a multistoried building. A is dropped from 100 m and after some time B is dropped from 50 m height. Both of them reach the earth at the same time. Will they have equal velocity while reaching the ground ? Calculate and find out the answer (take g =10 m/s
2).
Q 11.
Can you calculate density of Earth from Newton’s law of gravitation ?
Q 12.
Fill in the blanks :
________ of an object is the force of gravity acting on it.
Q 13.
The mass of Earth is
kg and that of moon is
kg. If the distance between the Earth and the Moon is
km, calculate the force exerted by Earth on the Moon. Given G =
.
Q 14.
Who measured the value of G first time, experimentally?
Q 15.
At what height above the surface of the earth, the value of 'g' becomes 64% of its value at the surface of the earth. Take radius of the earth = 6400 km.
Q 16.
Why is G called the Universal Constant?
Q 17.
What is the SI unit of weight ?
Q 18.
State and explain universal law of gravitation given by Newton.What is the importance of this law
Q 19.
Does the force of attraction between two objects depend on the properties of intervening medium?
Q 20.
The tangential velocity of a planet or moon moving in a circle is at a right angle to ____________. (fill in the blank)
Q 22.
Loaded test-tube placed in pure milk sinks to a certain mark (M). Now some water is mixed with the milk. Will the test tube sink more or less? Explain.
Q 23.
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 24.
Suppose a planet exists whose mass and radius both,are half those of Earth.Calculate the acceleration due to gravity on the surface of this planet.
Q 25.
State the universal law of gravitation.
Q 26.
What is the importance of universal law of gravitation ?
Q 27.
Does Newton’s third law of motion apply to gravitational force ?
Q 28.
A body weighs 10 kg on the surface of earth.What would be its mass and weight at the centre of earth ?
Q 29.
Fill in the blanks :
The value of Universal Gravitation constant (G) is ________ Nm
2kgs
-2.
Q 30.
Fill in the blanks :
The acceleration which causes changes only in direction of the velocity of a body is called __________ and it is always directed ___________ the circle.
Q 31.
The gravitational force between two objects is 100 N. How should the distance between these objects be changed so that force between them becomes 50 N ?
Q 32.
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 33.
A force of 20 N acts upon a body whose weight is 9.8 N.What is the mass of the body and how much is its acceleration ?
Q 34.
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 35.
What is the acceleration of free fall ?
Q 36.
What is the source of centripetal force that a planet requires to revolve around the Sun ? On what factors does that force depend ?
Q 37.
Which force revolves Moon around Earth ?
Q 38.
Which force accelerates a body in free fall ?
Q 39.
What is value of ‘g’ on Earth ?
Q 40.
What is the weight of a body of mass 1 kg on Earth ?
Q 41.
Can a body have weight but no mass ?
Q 42.
Distinguish between mass and weight.
Q 43.
On earth,value of G =
.What is its value on moon,where g is nearly
th that of earth ?
Q 44.
Fill in the blanks :
Geocentric model i.e. the Earth is the orbital centre of all celestial bodies was proposed by _____.
Q 45.
Fill in the blanks :
The force which keeps the object moving in a circular path is called _____ force. It always acts towards the _____.
Q 46.
Fill in the blanks :
Kepler's Law of ______ states that a line that connects a planet to the Sun sweeps out equal ______ in the plane of the planet's orbit in _____time intervals.
Q 47.
Fill in the blanks :
Acceleration due to gravity (g) is _______ (dependent/independent) of mass.
Q 48.
What are the Kepler Laws that govern the motion of the planets?
Q 49.
How is gravitational force of attraction between two bodies affected if(i) Mass of both bodies is doubled.(ii) Distance between them is halved.
