Question:
Explain what is meant by ‘free fall’and acceleration due to gravity.
Answer:
Refer to Art 3.11, Page 159.
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.
Why do sewing needles and all pins have a sharp pointed tip?
Q 4.
Calculate the value of acceleration due to gravity on Moon. Given mass of Moon =
kg, radius of Moon = 1740 km
Q 5.
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 6.
Fill in the blanks :
Every object in the universe ________ other bodies.
Q 7.
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 8.
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 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.
Which force is responsible for tides in the ocean at night ?
Q 11.
What do we call the gravitational force between the Earth and an object ?
Q 12.
What is the value of ‘g’ at the centre of Earth ?
Q 13.
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 14.
What do you mean by acceleration due to gravity ?
Q 15.
Can you calculate density of Earth from Newton’s law of gravitation ?
Q 16.
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 17.
State and explain universal law of gravitation given by Newton.What is the importance of this law
Q 18.
Who measured the value of G first time, experimentally?
Q 19.
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 20.
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 21.
What is the gravitational acceleration of a spaceship at a distance equal to two Earth’s radius from the centre of the Earth ?
Q 22.
Write the standard equations of motion when an object is thrown upwards with some initial velocity?
Q 23.
Fill in the blanks :
________ of an object is the force of gravity acting on it.
Q 24.
What is the importance of universal law of gravitation ?
Q 25.
Fill in the blanks :
The value of
g at poles is ______ (lower/higher) than its value at the equator.
Q 26.
Fill in the blanks :
Heliocentric model was proposed by ______.
Q 28.
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 29.
What happens to 'g' experienced by a body when it moves up the earth's surface?
Q 31.
Fill in the blanks :
The gravitational force between the earth and the object is generally called ____________.
Q 32.
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 33.
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 34.
Does Newton’s third law of motion apply to gravitational force ?
Q 35.
What was geocentric model? Who proposed this theory?
Q 36.
Who explained the motion of planets around the Sun ?
Q 37.
Compare gravitational force between light objects and heavy objects.
Q 38.
Fill in the blanks :
Weight of an object is the product of ______ and ________.
Q 39.
What are the differences between the mass of an object and its weight?
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 41.
Why is it difficult to hold a school bag having a strap made of a thin and strong string?
Q 42.
Is the Archimedes principle applicable to gases?
Q 43.
Relative density of silver is 10.8. If the density of water is 10
3kg/m
3, find density of silver.
Q 44.
The volume of 50g of a substance is 20 cm
3. If the density of water is 1g/cm
3, will the substance float or sink?
Q 45.
If the distance of Earth from the Sun were half the present value,how many days will make one year ?
Q 46.
A force of 2 kg wt. acts on a body of mass 4.9 kg.Calculate its acceleration
Q 47.
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 48.
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 49.
Distinguish between mass and weight.
Q 50.
Comment on application of Newton’s third law of motion to gravitation.Illustrate by examples.
