Question:
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?
Answer:
Since we know that, Time of Ascent = Time of Descent.
⇒ Time taken by ball to reach highest point = 4 /2 = 2s
Let u be the initial velocity the ball is thrown upwards.
At its highest point (h), final velocity (v) = 0 m/s
Using equation v = u + at
⇒ 0 = u - 2g
⇒ u = 2 × 9.8 = 19.6 m/s
The ball was thrown with initial velocity 19.6 m/s
Maximum height it will reach,
h = ut - ½gt2
⇒ h = 19.6 × 2 - ½ × 9.8 × 22 = 19.6 × 2 - 19.6 = 19.6 m
After t = 3 seconds, the distance traveled will be
h3 = ut - ½gt2 = 19.6 × 3 - ½ × 9.8 × 32 = 58.8 - 44.1 = 14.7 m wrt ground.
Ball's position w.r.t. to its high point = 19.6 - 14.7 = 4.9m
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.
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 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.
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.
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 8.
Fill in the blanks :
Every object in the universe ________ other bodies.
Q 9.
What is the value of ‘g’ at the centre of Earth ?
Q 10.
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 11.
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 12.
What do you mean by acceleration due to gravity ?
Q 13.
Which force is responsible for tides in the ocean at night ?
Q 14.
State and explain universal law of gravitation given by Newton.What is the importance of this law
Q 15.
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 16.
What do we call the gravitational force between the Earth and an object ?
Q 17.
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 18.
Can you calculate density of Earth from Newton’s law of gravitation ?
Q 19.
Fill in the blanks :
________ of an object is the force of gravity acting on it.
Q 20.
Fill in the blanks :
The value of
g at poles is ______ (lower/higher) than its value at the equator.
Q 22.
Fill in the blanks :
Heliocentric model was proposed by ______.
Q 23.
Who measured the value of G first time, experimentally?
Q 24.
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 25.
What is the gravitational acceleration of a spaceship at a distance equal to two Earth’s radius from the centre of the Earth ?
Q 26.
The distance between two objects is doubled. What happens to gravitational force between them
Q 27.
Fill in the blanks :
The value of
g on the earth's surface is ______.
Q 28.
What are the Kepler Laws that govern the motion of the planets?
Q 29.
What happens to 'g' experienced by a body when it moves up the earth's surface?
Q 30.
Write the standard equations of motion when an object is thrown upwards with some initial velocity?
Q 32.
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 33.
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 34.
Write the formula to find the magnitude of the gravitational force between the Earth and an object on the surface of the Earth.
Q 35.
What is the importance of universal law of gravitation ?
Q 36.
Why will a sheet of paper fall slower than one that is crumpled into a ball ?
Q 37.
What is value of ‘g’ on Earth ?
Q 38.
How are gravitation and gravity related ?
Q 39.
Can you calculate mass of Earth from Newton’s law of gravitation ?
Q 40.
State and explain universal law of gravitation.What is its importance ?
Q 41.
On earth,value of G =
.What is its value on moon,where g is nearly
th that of earth ?
Q 42.
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 ?
Q 43.
Fill in the blanks :
Weight of an object is the product of ______ and ________.
Q 44.
State the universal law of gravitation.
Q 45.
When a ball is thrown upwards, it falls back to the ground. Name the force which makes it fall.
Q 46.
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 47.
Fill in the blanks :
Universal gravitational constant G = _____________.
Q 48.
A cuboid room has dimensions 50m x 15m x 3.5m. What is the mass of the air enclosed in the room if the density of air = 1.30 kg/m
3.
Q 49.
A stone drops from the edge of the roof.It passes a window 2 m high in 0.1 s.How far is the roof above the top of the window
Q 50.
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 ?
