Question:
A ball is thrown vertically upwards with a velocity of 49 m/s. Calculate(i) the maximum height to which it rises.(ii)the total time it takes to return to the surface of the earth.
Answer:
Given, initial velocity (u) = 49 m/s
final velocity the ball reaches max. height (v) = 0 m/s
acceleration due to gravity (g) = -9.8 m/s2.
g is -ve because it opposed the vertical motion.
height (h) ball will reach = ? m
Time of ascent i.e. time taken to reach max. height (t) = ? s
Using equation v2 - u2 =2aS,
⇒ 02 - 492 = -2(9.8)h
⇒ h = (49 × 49)/19.6 = 490/4 = 122.5 m
Using equation v = u + at i.e. 0 = 49 - 9.8t
⇒ t = 49/9.8 = 5s
Since Time of ascent = Time of descent.
Total time the ball will take to reach ground = 5 + 5 = 10s
Gravitation
Q 1.
State Kepler’s Laws of planetary motion. How did Newton guess inverse square law ?
Q 2.
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 3.
Can you calculate density of Earth from Newton’s law of gravitation ?
Q 4.
What do we call the gravitational force between the Earth and an object ?
Q 5.
What is the value of ‘g’ at the centre of Earth ?
Q 6.
What do you mean by acceleration due to gravity ?
Q 7.
Why do sewing needles and all pins have a sharp pointed tip?
Q 8.
Fill in the blanks :
Weight of an object is the product of ______ and ________.
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.
Fill in the blanks :
Every object in the universe ________ other bodies.
Q 11.
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 12.
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 13.
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 14.
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 15.
Is weight a scalar quantity?
Q 16.
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 17.
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 ?
Q 18.
Fill in the blanks :
The gravitational force between the earth and the object is generally called ____________.
Q 19.
Calculate the value of acceleration due to gravity on Moon. Given mass of Moon =
kg, radius of Moon = 1740 km
Q 20.
A stone falling towards Earth also attracts the Earth with the same force.Is it true ?
Q 21.
On earth,value of G =
.What is its value on moon,where g is nearly
th that of earth ?
Q 22.
Fill in the blanks :
Heliocentric model was proposed by ______.
Q 23.
Define weight? How it is related to mass?
Q 24.
Mass of an object is 10 kg. What is its weight on the Earth? (g = 9.8 m/s
2.)
Q 27.
What are Plimsoll Lines?
Q 28.
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 29.
Define g and G.Establish relation between them.
Q 30.
Fill in the blanks :
The value of Universal Gravitation constant (G) is ________ Nm
2kgs
-2.
Q 31.
Fill in the blanks :
The value of
g on the earth's surface is ______.
Q 32.
Fill in the blanks :
The value of
g ________ (increases/decreases) as we go upwards from the earth's surface.
Q 33.
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 34.
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 35.
Write the standard equations of motion when an object is thrown upwards with some initial velocity?
Q 36.
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 37.
Is mass a scalar quantity?
Q 38.
Fill in the blanks :
The SI unit of mass is ______.
Q 39.
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 40.
What do you mean by Thrust or Buoyant force?
Q 41.
The volume of 50 g of a substance is 20 cm
3. If the density of water is 1 g cm
-3, will the substance float or sink?
Q 42.
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 43.
What is the gravitational acceleration of a spaceship at a distance equal to two Earth’s radius from the centre of the Earth ?
Q 44.
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 45.
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 46.
Why will a sheet of paper fall slower than one that is crumpled into a ball ?
Q 47.
What is the value of G (i) on Earth (ii) on Moon ?
Q 48.
The distance between two objects is doubled. What happens to gravitational force between them
Q 49.
Which force accelerates a body in free fall ?
Q 50.
Who gave three laws of planetary motion ?
