Q1 How does the force of gravitation between two objects change when the distance between them is reduced to half ?... Q2 Gravitational force acts on all objects in proportion to their masses. Why then, a heavy object does not fall fas... Q3 What is the magnitude of the gravitational force between the earth and a 1 kg object on its surface? (Mass of the... Q4 The earth and the moon are attracted to each other by gravitational force. Does the earth attract the moon with a... Q5 If the moon attracts the earth, why does the earth not move towards the moon?... Q6 What happens to the force between two objects, if (i) the mass of one object is doubled? (ii) the distance betw... Q7 What is the importance of universal law of gravitation?... Q8 What is the acceleration of free fall?... Q9 What do we call the gravitational force between the earth and an object?... Q10 Amit buys few grams of gold at the poles as per the instruction of one of his friends. He hands over the same whe... Q11 Why will a sheet of paper fall slower than one that is crumpled into a ball?... Q12 Gravitational force on the surface of the moon is only 1/6 as strong as gravitational force on the earth. What is... Q13 A ball is thrown vertically upwards with a velocity of 49 m/s. Calculate (i) the maximum height to which it rise... Q14 A stone is released from the top of a tower of height 19.6 m. Calculate its final velocity.... Q15 A stone is thrown vertically upward with an initial velocity of 40 m/s. Taking g = 10 m/s2, find the maximum heig... Q16 Calculate the force of gravitation between the earth and the Sun, given that the mass of the earth = 6 × 10... Q17 A stone is allowed to fall from the top of a tower 100 m high and at the same time another stone is projected ver... Q18 A ball thrown up vertically returns to the thrower after 6 s. Find (a) the velocity with which it was thrown up,... Q19 In what direction does the buoyant force on an object immersed in a liquid act?... Q20 Why does a block of plastic released under water come up to the surface of water?... Q21 The volume of 50 g of a substance is 20 cm3. If the density of water is 1 g cm-3, will the substance float or sin... Q22 The volume of a 500 g sealed packet is 350 cm3. Will the packet float or sink in water if the density of water is...
Question 6
Answer
According to the universal law of gravitation,
(i) Force is directly proportional to the masses of the objects. If the mass of one object is doubled, then the gravitational force will also get doubled.
(ii) Force is inversely proportional to the square of the distances between the objects. If the distance is doubled, then the gravitational force becomes one-fourth.
Similarly, if the distance is tripled, then the gravitational force becomes one-ninth.
(iii) Force is directly proportional to the product of masses of the objects. If the masses of both the objects are doubled, then the gravitational force becomes four times.
Popular Questions of Class 9 Science
- Q:-
Abdul, while driving to school, computes the average speed for his trip to be 20 km h-1. On his return trip along the same route, there is less traffic and the average speed is 40 km h-1. What is the average speed for Abdul’s trip?
- Q:-
An object of mass 40 kg is raised to a height of 5 m above the ground. What is its potential energy? If the object is allowed to fall, find its kinetic energy when it is half-way down.
- Q:-
A driver of a car travelling at 52 km h-1 applies the brakes and accelerates uniformly in the opposite direction. The car stops in 5 s. Another driver going at 3 km h-1 in another car applies his brakes slowly and stops in 10 s. On the same graph paper, plot the speed versus time graphs for the two cars. Which of the two cars travelled farther after the brakes were applied?
- Q:-
Fig 8.11 shows the distance-time graph of three objects A,B and C. Study the graph and answer the following questions:
Fig. 8.11
(a) Which of the three is travelling the fastest? (b) Are all three ever at the same point on the road? (c) How far has C travelled when B passes A?
(d) How far has B travelled by the time it passes C?
- Q:-
Two objects, each of mass 1.5 kg, are moving in the same straight line but in opposite directions. The velocity of each object is 2.5 m s-1 before the collision during which they stick together. What will be the velocity of the combined object after collision?
- Q:-
Soni says that the acceleration in an object could be zero even when several forces are acting on it. Do you agree with her? Why?
- Q:-
How do poriferan animals differ from coelenterate animals?
- Q:-
Two objects of masses 100 g and 200 g are moving along the same line and direction with velocities of 2 m s-1 and 1 m s-1, respectively. They collide and after the collision, the first object moves at a velocity of 1.67 m s-1. Determine the velocity of the second object.
- Q:-
The speed-time graph for a car is shown is Fig. 8.12.
Fig. 8.12
(a) Find how far does the car travel in the first 4 seconds. Shade the area on the graph that represents the distance travelled by the car during the period.
(b) Which part of the graph represents uniform motion of the car? - Q:-
How are sol, solution and suspension different from each other?
Recently Viewed Questions of Class 9 Science
- Q:-
An artificial satellite is moving in a circular orbit of radius 42250 km. Calculate its speed if it takes 24 hours to revolve around the earth.
- Q:-
An object of mass 40 kg is raised to a height of 5 m above the ground. What is its potential energy? If the object is allowed to fall, find its kinetic energy when it is half-way down.
- Q:-
Two objects, each of mass 1.5 kg, are moving in the same straight line but in opposite directions. The velocity of each object is 2.5 m s-1 before the collision during which they stick together. What will be the velocity of the combined object after collision?
- Q:-
Abdul, while driving to school, computes the average speed for his trip to be 20 km h-1. On his return trip along the same route, there is less traffic and the average speed is 40 km h-1. What is the average speed for Abdul’s trip?
- Q:-
Which wave property determines
(a) loudness, (b) pitch? - Q:-
A hammer of mass 500 g, moving at 50 m s-1, strikes a nail. The nail stops the hammer in a very short time of 0.01 s. What is the force of the nail on the hammer?
- Q:-
Diagrammatically show the difference between the three types of muscle fibres.
- Q:-
A driver of a car travelling at 52 km h-1 applies the brakes and accelerates uniformly in the opposite direction. The car stops in 5 s. Another driver going at 3 km h-1 in another car applies his brakes slowly and stops in 10 s. On the same graph paper, plot the speed versus time graphs for the two cars. Which of the two cars travelled farther after the brakes were applied?
- Q:-
A mass of 10 kg is at a point A on a table. It is moved to a point B. If the line joining A and B is horizontal, what is the work done on the object by the gravitational force? Explain your answer.
- Q:-
For the symbol H,D and T tabulate three sub-atomic particles found in each of them.
-
Answer:
From the relationship,
(i) If the mass of one object (say body 1) is doubled, thenThus, the gravitational force between the two objects gets doubled. (ii) If the distance between the two objects is doubled, thenThus, the gravitational force between the two objects becomes one-fourth. If the distance between the two objects is tripled, thenThus, the gravitational force between the two objects becomes one-ninth. (iii) If the masses of both the objects are doubled, thenThus, the gravitational force between the two objects becomes 4 times.
warning Report Error
Page 2
-
Answer:
Universal law of gravitation is important as it accounts, (a) for the existence of the solar system, i.e., motion of planets around the sun. (b) for holding the atmosphere near the surface of the earth. (c) for the flow of water in rivers. (d) for rainfall and snowfall. (e) for occurrence of tides.
warning Report Error
Page 3
-
Answer:
All objects moving towards earth on account of gravitational force of earth on them are said to be in free fall. This force produces a uniform acceleration in the object. This is acceleration of free fall and its value is 9.8 ms-2 .
warning Report Error
Page 4
-
Answer:
The gravitational force between the earth and an object is called the force of gravity or simply earth’s gravity.
warning Report Error
Page 5
-
Answer:
We know that the value of g is greater at the poles than at the equator. So the weight of gold at the equator will be less than the weight of gold at the poles. So it is obvious that the friend at equator will not agree with the weight of gold bought at poles.
warning Report Error
Page 6
-
Answer:
The sheet of paper falls slower than one that is crumpled into a ball because in first case the area of the sheet is more so it experiences large opposing force due to air. While the sheet crumpled into a ball experience less opposing force due to small area.
warning Report Error
Page 7
-
Answer:
Here, m = 10 kg Mass is the same on earth and moon. Now, weight of the object on earth
Weight of the object on moon,
warning Report Error
Page 8
-
Answer:
Initial velocity, u = 49 m/s Acceleration, a = g = - 9.8 m/s2 Velocity at the highest point, v = 0 m/s (i) If h is the maximum height reached by the ball, then
orThus, the ball will reach a height of 122.5 m. We have,Here,Total time
warning Report Error
Page 9
-
Answer:
Initial velocity,
Final velocity,Height of the tower,Acceleration due to gravity,Using the equation,
warning Report Error
Page 10
-
Answer:
Here,
FromorAs final position of the stone coincides with its initial position, net displacement = 0 Total distance covered by the stone
warning Report Error
Page 11
-
Answer:
Mass of the earth,
Mass of the sun,Distance between the earth and the sun,Then, the gravitational force between the earth and the sun is given by,Thus, the earth and the sun attract each other by a gravitational force of
warning Report Error
Page 12
-
Answer:
Here, h = 100 m. Let the two stones meet after t seconds at a point P which is at a height x above the ground as shown in figure.For stone 1,
From.....(i) For stone 2,From......(ii) Adding equations (i) and (ii)
warning Report Error
Page 13
-
Answer:
Here, time of ascent = time of descent,
(a)From(b) From(c)ball is at maximum height. From(below the top)
warning Report Error
Page 14
-
Answer:
When the object has density less than 1 g cm-1 then it floats on the surface of water, because, it always displaces more weight of water than its own weight. As buoyant force is more than its own weight, therefore, it floats. When the object has density more than 1 g cm-3 then it sinks in water, because it always displaces less weight of water than its own weight. As buoyant force is less than its own weight, therefore, it sinks.
warning Report Error
Page 15
-
Answer:
In fact, a weighing machine is a sort of spring balance which measure the weight (and not the mass) of a body. When we stand on the weighing machine, our weight (which is due to gravitational attraction of the earth) acts vertically downwards. But the buoyancy due to air on our body acts vertically upwards. As a result of this, our apparent weight (true weight buoyant force) is less than the true weight Since the weighing machine measures the apparent weight, our true weight is more, i.e., more than 42 kg.
warning Report Error
Page 16
-
Answer:
We know that true weight = apparent weight + up thrust. The cotton bag is heavier than the iron bar. This is due to the reason, that the bag of cotton which has more volume (as it has less density) than the iron bar (which has more density), experiences more up thrust due to air.
warning Report Error
Page 17
-
Answer:
If an object is immersed in a liquid then the buoyant force due to liquid acts on the object in vertically upward direction.
warning Report Error
Page 18
-
Answer:
The buoyant force acting on the block of plastic is more than its weight. As a result of this, it comes up when released under water. The cause of this larger buoyant force on the block of plastic is due to its density being smaller than that of water.
warning Report Error
Page 19
-
Answer:
Density of water
Mass of substanceVolume of substanceDensity of substanceAs the density of the substance is greater than that of water, the given substance will sink in water.
warning Report Error
Page 20
-
Answer:
Here, mass of packet, M = 500 g volume of the packet, V = 350 cm3 Clearly, density of packet,
Since the density of packet is more than density of water, the packet will sink. As the packet is fully submerged in water, mass of water displaced by the packet = volume of the packet x density of water = (350 cm3) x (1 g/cm3) = 350 g
warning Report Error
Page 21
-
Answer:
(d) Objects of different masses falling freely near the surface of the moon would have the same velocities at any instant because they will have same acceleration due to gravity.
warning Report Error
Page 22
-
Answer:
(c) It is least at the equator and maximum at the poles due to rotation of earth i.e., it is given by
At poles, So g maximum At equator, So g maximum
warning Report Error
Page 23
-
Answer:
(a) We know that, according to force of gravitation
(G= Gravitational constant) whereandare the masses of two objects respectively. And r is the distance between the two masses Now, according to the question, if masses of both objects are halved, i.e.,andNew forcewhereSo, new forceThus, the new gravitational force will becometimes of its original gravitational force.
warning Report Error
Page 24
-
Answer:
(c) In circular motion, the direction of velocity at a point is always along the tangent at that point. If string breaks, then the centripetal force acting on the stone becomes zero and it will move along a straight line tangential to the circular path.
whereare the velocities point A, B, C, D in circular path.
warning Report Error
Page 25
-
Answer:
(d) In a liquid of higher density more part of the object remains outside the liquid. Since, the order of part of their volume outside the liquid is given by (part of the body outside the liquid) a- densities of liquid
Thus, the order of densities in increasing order is
warning Report Error
Page 26
-
Answer:
(d) The quantity G is universal constant of nature. It is applied to all the body present in universe It is constant of proportionality in Newton's universal law of gravitation. The accepted value of G is
warning Report Error