Question:
In Fig.,the line that joins a planet to the sun sweeps out areas
,
in time intervals 6 weeks,3 weeks and 2 weeks respectively.How are
,
realted ?
Answer:
According to Kepler’s 2nd law, areal velocity of planet is constant.
∴== or ==
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.
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 4.
Calculate the value of acceleration due to gravity on Moon. Given mass of Moon =
kg, radius of Moon = 1740 km
Q 5.
Which force is responsible for tides in the ocean at night ?
Q 6.
What is the value of ‘g’ at the centre of Earth ?
Q 7.
Why do sewing needles and all pins have a sharp pointed tip?
Q 8.
Fill in the blanks :
Every object in the universe ________ other bodies.
Q 9.
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 10.
Fill in the blanks :
________ of an object is the force of gravity acting on it.
Q 11.
What do you mean by acceleration due to gravity ?
Q 12.
Can you calculate density of Earth from Newton’s law of gravitation ?
Q 13.
Who measured the value of G first time, experimentally?
Q 14.
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 15.
Does the force of attraction between two objects depend on the properties of intervening medium?
Q 16.
Calculate the force of gravitation between two objects of masses 80 kg and 1200 kg kept at a distance of 10 m from eachother.Given, G =
/
.
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.
Fill in the blanks :
The SI unit of mass is ______.
Q 20.
Why will a sheet of paper fall slower than one that is crumpled into a ball?
Q 21.
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 22.
What is the source of centripetal force that a planet requires to revolve around the Sun ? On what factors does that force depend ?
Q 23.
Which force revolves Moon around Earth ?
Q 24.
What was geocentric model? Who proposed this theory?
Q 25.
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 26.
In what direction does the buoyant force on an object immersed in a liquid act?
Q 27.
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 28.
What do we call the gravitational force between the Earth and an object ?
Q 29.
Who explained the motion of planets around the Sun ?
Q 30.
Does value of ‘g’ vary from place to place on Earth ?
Q 31.
What is the SI unit of mass ?
Q 32.
Can a body have weight but no mass ?
Q 33.
Distinguish between gravitation and gravity.
Q 34.
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 35.
A ball is thrown with some velocity 'u' m/s. Show that under free fall, it will fall the ground with same velocity.
Q 37.
The tangential velocity of a planet or moon moving in a circle is at a right angle to ____________. (fill in the blank)
Q 38.
Fill in the blanks :
A body is said to be in _______ when only gravity acts on it.
Q 39.
Fill in the blanks :
During free fall condition, the body is in state of __________.
Q 40.
Fill in the blanks :
All other variables remaining constant, the force of gravitation is ________ proportional to the square of distance between the two objects.
Q 41.
Fill in the blanks :
Assuming negligible air drag, if a steel ball and a table tennis ball are dropped from a height of 100 metres, both will reach the ground at ________ time(s). (same/different)
Q 42.
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 43.
What do you mean by Thrust or Buoyant force?
Q 44.
You find your mass to be 42 kg on a weighing machine. Is your mass more or less than 42 kg?
Q 45.
Two electrons each of mass
kg are at a distance of 10 A.Calculate the gravitational force of attraction between them. Given 1 A =
m.
Q 46.
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 47.
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 48.
A car falls off a ledge and drops to the ground in 0.5 s.Let g =
(for simplifying the calculations).
(i) What is its speed on striking the ground ?
(ii) What is its average speed during 0.5 s ?
(iii) How high is the ledge from the ground ?
Q 49.
State the universal law of gravitation.
Q 50.
Write the formula to find the magnitude of the gravitational force between the Earth and an object on the surface of the Earth.
