Question:
What is free fall?
Answer:
The falling of a body from height towards the earth under the influence of gravitation force of the earth alone only is called free fall.
Gravitation
Q 1.
Two objects of masses
having the same size are dropped simultaneously from heights
respectively.Find out the ratio of time they would take in reaching the ground.Will this ratio remain the same if (1) one of the objects is hollow and the other one is solid and (ii) both of them are hollow,size remaining the same in each case.Give reason.
Q 2.
Can you calculate density of Earth from Newton’s law of gravitation ?
Q 3.
Write the standard equations of motion when an object is thrown upwards with some initial velocity?
Q 4.
State and explain universal law of gravitation.What is its importance ?
Q 5.
Comment on application of Newton’s third law of motion to gravitation.Illustrate by examples.
Q 6.
Does gravitational force between two objects depend on medium between them ?
Q 7.
What is the SI unit of weight ?
Q 8.
How are gravitation and gravity related ?
Q 9.
Distinguish between mass and weight.
Q 10.
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 11.
What are the differences between the mass of an object and its weight ?
Q 12.
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 13.
What do you mean by acceleration due to gravity ?
Q 14.
What do we call the gravitational force between the Earth and an object ?
Q 15.
What is inverse square rule ?
Q 16.
Calculate the force of gravitation between the Earth and the Sun,given that the mass of the Earth =
kg and mass of the Sun =
kg. The average distance between the two is
m.
Q 17.
Explain what is meant by ‘free fall’and acceleration due to gravity.
Q 18.
Two particles of equal mass (m) move in a circle of radius (r) under the action of their mutual gravitational attraction. Find the speed of each particle.
Q 19.
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 21.
Why do sewing needles and all pins have a sharp pointed tip?
Q 22.
What is the gravitational acceleration of a spaceship at a distance equal to two Earth’s radius from the centre of the Earth ?
Q 23.
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 24.
What is the usual shape of orbits of planets around the Sun ?
Q 25.
In free fall, will heavier objects accelerate more than light ones ?
Q 26.
Write down the equations of motion of objects under the influence of gravitational force of Earth.Explain the meaning of the symbols used.
Q 27.
State Kepler’s Laws of planetary motion. How did Newton guess inverse square law ?
Q 28.
Gravitational force on the surface of the moon is only 1/6th as strong as gravitational force on the Earth. What is the weight in newtons of a 10 kg object on the moon and on the Earth? What is the value of 'g' at the surface of the moon?
Q 29.
A stone is released from the top of a tower of height 19.6 m. Calculate its final velocity just before touching the ground.
Q 31.
Fill in the blanks :
________ of an object is the force of gravity acting on it.
Q 32.
The weight of a man is 690N which contains 5.3 x 10
-3 m
3 of blood. Find (a) blood's weight. Take density of blood is 1060 kg/m
3 (b) express it as a percentage of body weight.
Q 33.
Why will a sheet of paper fall slower than one that is crumpled into a ball?
Q 34.
If the distance of Earth from the Sun were half the present value,how many days will make one year ?
Q 35.
An object is thrown vertically upwards and rises to a height of 10 m. Calculate (i) the velocity with which the object was thrown upwards and (ii) the time taken by the object to reach the highest point.
Q 36.
Which force accelerates a body in free fall ?
Q 37.
Why don’t two objects move towards each other due to gravitational pull between them ?
Q 38.
Can a body have weight but no mass ?
Q 39.
Fill in the blanks :
Acceleration due to gravity (g) is _______ (dependent/independent) of mass.
Q 40.
Fill in the blanks :
Weight of an object is the product of ______ and ________.
Q 41.
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.
Q 42.
A ball is thrown up and is caught by the player after 4 seconds.How high did it go and with what velocity was it thrown? How far below the ball will be from its highest point after 3 seconds from start?
Q 43.
Fill in the blanks :
Motion of body with constant speed in a circular path is called ______________.
Q 44.
What do you mean by Thrust or Buoyant force?
Q 45.
The weight of an empty glass is 1 N. When completely filled with water, the glass weighs 4 N. If you now throw the water away and fill the glass partly with sand, the weight becomes 4 N. If the rest of the glass is now filled up with water, the weight becomes 6 N. What is the relative density of sand?
Q 46.
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 47.
If the distance between two masses is increased by a factor of 4,by what factor would the mass of one of them have to be altered to maintain the same gravitational force ?
Q 48.
What do you mean by free fall ?
Q 49.
A body is projected upwards. What is its velocity at maximum height
Q 50.
What is the weight of a body of mass 1 kg on Earth ?
