Question:
A physics teacher explains to his students in class,the subject of motion under gravity.When a body is projected upwards from the ground with a certain velocity a,the velocity goes on decreasing at a constant rate due to gravitational pull of earth.At a certain height,this velocity becomes zero.The body cannot rise further.From this maximum height,the body begins to fall and its velocity goes on increasing at the same constant rate due to gravitational pull of earth.The body would strike the ground with exactly the same velocity (v = u),with which it was thrown initially. This is on the assumption that resistance due to air is zero, either way.
Read the above passage and answer the following questions:
(i) Why is velocity of body on striking the ground the same as initial velocity of projection of the body ?
(ii) Does the body take same time to fail to ground as the time it takes to reach the maximum height ?
(iii) What values of life do you learn from this brief study ?
Answer:
(i) The two velocities are equal in accordance with the principle of conservation of energy.During the upward journey,kinetic energy of the body is converted into its potential energy.And during the downward journey of the body,potential energy is converted back into the same kinetic energy.Of course, we assume that there are no stray losses of energy.
(ii) Yes, time taken to fall to ground from maximum height = time taken to go from ground to the maximum height,
(iii) From this brief study, we learn that output can at the most be equal to input,i.e., the degree of our success is always commensurate with our efforts.We reap what we harvest.The degree of sweetness is determined by the amount of sugar we put in.
Gravitation
Q 1.
State Kepler’s Laws of planetary motion. How did Newton guess inverse square law ?
Q 2.
Why do sewing needles and all pins have a sharp pointed tip?
Q 3.
Calculate the value of acceleration due to gravity on Moon. Given mass of Moon =
kg, radius of Moon = 1740 km
Q 4.
Fill in the blanks :
Every object in the universe ________ other bodies.
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.
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 7.
Which force is responsible for tides in the ocean at night ?
Q 8.
What is the value of ‘g’ at the centre of Earth ?
Q 9.
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 10.
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 11.
What do we call the gravitational force between the Earth and an object ?
Q 12.
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 13.
What do you mean by acceleration due to gravity ?
Q 14.
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 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.
Write the standard equations of motion when an object is thrown upwards with some initial velocity?
Q 21.
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 22.
What is the importance of universal law of gravitation ?
Q 23.
Fill in the blanks :
________ of an object is the force of gravity acting on it.
Q 24.
Fill in the blanks :
Heliocentric model was proposed by ______.
Q 25.
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 26.
What is the gravitational acceleration of a spaceship at a distance equal to two Earth’s radius from the centre of the Earth ?
Q 27.
Fill in the blanks :
Weight of an object is the product of ______ and ________.
Q 29.
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 31.
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 32.
What was geocentric model? Who proposed this theory?
Q 33.
What happens to 'g' experienced by a body when it moves up the earth's surface?
Q 34.
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 35.
Fill in the blanks :
The value of
g at poles is ______ (lower/higher) than its value at the equator.
Q 36.
Fill in the blanks :
The gravitational force between the earth and the object is generally called ____________.
Q 37.
Who explained the motion of planets around the Sun ?
Q 38.
What is the SI unit of weight ?
Q 39.
Define weight? How it is related to mass?
Q 40.
Is weight a scalar quantity?
Q 41.
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 42.
Does Newton’s third law of motion apply to gravitational force ?
Q 43.
Distinguish between mass and weight.
Q 44.
(a) What is the relationship between g and G?
(b) Show mathematically whether g (acceleration due to gravity on the earth) depends on the mass of the object itself or not.
(c) Show that for a given location on the surface of the earth g is almost constant.
Q 46.
As you climb up a mountain, your ears “pop” because of the changes in atmospheric pressure. In which direction, outward or inward, does your eardrum move when you climb up?
Q 47.
Relative density of silver is 10.8. If the density of water is 10
3kg/m
3, find density of silver.
Q 48.
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 49.
Mass of an object is 10 kg. What is its weight on Earth ?
Q 50.
A stone is released from the top of a tower of height 19.6 m.Calculate its final velocity just before touching the ground.
