Question:
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 ?
Answer:
(i) At the highest point,velocity of body = zero,and acceleration of body = + g = ,in the downward direction.
(ii) Here,u=,a = - g = -.
5 = h = ?, v = 0
From = 2 as ; 0 - = 2 (- 9.8)h
h==19.6 m
(iii) The upward motion of a body is opposed by gravitational pull of earth. Similarly,your progress and prosperity in life are opposed by so many factors. Just as a body has to work against gravity for rising.upwards,every iodividual has 10 work against many odds and obstacles to rise in life. Consistent efforts alone can surmount the impediments and help you achieve your goal.
Gravitation
Q 1.
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 2.
Can you calculate density of Earth from Newton’s law of gravitation ?
Q 3.
What do we call the gravitational force between the Earth and an object ?
Q 4.
State Kepler’s Laws of planetary motion. How did Newton guess inverse square law ?
Q 5.
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 6.
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 7.
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 8.
What do you mean by acceleration due to gravity ?
Q 9.
What is the value of ‘g’ at the centre of Earth ?
Q 10.
Fill in the blanks :
Every object in the universe ________ other bodies.
Q 11.
Why do sewing needles and all pins have a sharp pointed tip?
Q 12.
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 13.
Fill in the blanks :
________ of an object is the force of gravity acting on it.
Q 14.
Calculate the value of acceleration due to gravity on Moon. Given mass of Moon =
kg, radius of Moon = 1740 km
Q 15.
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 16.
Calculate the force of gravitation between the earth and the Sun, given that the mass of the earth = 6 × 10
24 kg and of the Sun = 2 × 10
30 kg. The average distance between the two is 1.5 × 10
11 m.
Q 17.
What is the gravitational acceleration of a spaceship at a distance equal to two Earth’s radius from the centre of the Earth ?
Q 18.
Fill in the blanks :
Weight of an object is the product of ______ and ________.
Q 19.
Write the standard equations of motion when an object is thrown upwards with some initial velocity?
Q 20.
Fill in the blanks :
The gravitational force between the earth and the object is generally called ____________.
Q 21.
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 22.
Can a body have weight but no mass ?
Q 23.
Is weight a scalar quantity?
Q 24.
Who explained the motion of planets around the Sun ?
Q 25.
Does Newton’s third law of motion apply to gravitational force ?
Q 26.
What is inverse square rule ?
Q 27.
Fill in the blanks :
The value of
g ________ (increases/decreases) as we go upwards from the earth's surface.
Q 28.
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 29.
Define weight? How it is related to mass?
Q 30.
A force of 200 N acts on a surface of area 10 cm
2. Calculate thrust and pressure. How much the pressure changes if the area of contact increases to 50 cm
2.
Q 31.
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 32.
Which force is responsible for tides in the ocean at night ?
Q 33.
Explain what is meant by ‘free fall’and acceleration due to gravity.
Q 34.
Fill in the blanks :
The value of Universal Gravitation constant (G) is ________ Nm
2kgs
-2.
Q 35.
What are the Kepler Laws that govern the motion of the planets?
Q 36.
Who measured the value of G first time, experimentally?
Q 37.
How gravitational force is different from or similar to magnetic force (between two magnets) or coulomb force (between two charged object)?
Q 38.
How is gravitational force of attraction between two bodies affected if(i) Mass of both bodies is doubled.(ii) Distance between them is halved.
Q 39.
A stone is allowed to fall from the top of a tower 100 m high and at the same time another stone is projected vertically upwards from the ground with a velocity of 25 m/s. Calculate when and where the two stones will meet.
Q 40.
A ball is thrown upwards from the ground of a tower with a speed of 20 m/s. There is a window in the tower at the height of 15m from ground. How many times and when will the ball pass the window? (g = 10 m/s
2)
Q 42.
Fill in the blanks :
The force of gravity _________ with altitude. It also varies on the surface of the earth, _________ from poles to the equator.
Q 43.
The volume of a 500 g sealed packet is 350 cm
3. Will the packet float or sink in water if the density of water is 1 g cm
-3? What will be the mass of the water displaced by this packet?
Q 44.
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 45.
The distance of planet Jupiter from the sun is 5-2 times that of Earth.Find the period of revolution of Jupiter around sun.
Q 46.
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 47.
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 which the Moon attracts the Earth ? Why ?
Q 48.
Distinguish between gravitation and gravity.
Q 49.
Define g and G.Establish relation between them.
Q 50.
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.
