1.) Two objects of different masses falling freely near the surface of the moon would
Options:
a. Have same velocities at any instant
b. Have different acceleration
c. Experience force of same magnitude
d. Undergo a change in their inertia
Answer: a. Have same velocities at any instant
Explanation: In the absence of air resistance, all objects, regardless of their masses, fall with the same acceleration. Therefore, their velocities at any instant would also be the same.
2.) The value of acceleration due to gravity
Options:
a. Is same on equator and poles
b. Is least on poles
c. Is least on equator
d. Increases from poles to equator
Answer: c. Is least on equator
Explanation: The acceleration due to gravity is slightly less at the equator due to the centrifugal force caused by Earth’s rotation.
3.) A boy is whirling a stone tied to a string in a horizontal circular path. When the string breaks, the stone
Options:
a. Will continue to move in a circular path
b. Will move towards the center of the circular path
c. Will move tangentially
d. Will move perpendicular to the
Answer: c. Will move tangentially
Explanation: According to Newton’s first law, an object in motion tends to stay in motion along a straight line unless acted upon by a net external force. When the string breaks, the centripetal force disappears, and the stone will move tangentially to the circular path.
4.) The value of quantity G in the law of gravitation
Options:
a. Depends on the mass of Earth only
b. Depends on both mass and radius of Earth
c. Depends on the radius of Earth only
d. Independent of both mass and radius of Earth
Answer: d. Independent of both mass and radius of Earth
Explanation: The gravitational constant G is a universal constant and does not depend on the properties of individual objects like mass or radius.
5.) The atmosphere is held to the Earth by
Options:
a. Gravity
b. Wind
c. Cloud
d. Earth’s magnetic field
Answer: a. Gravity
Explanation: It is the gravitational pull of the Earth that holds the atmosphere in place.
6.) The weight of an object at the center of the Earth of radius R is
Options:
a. Zero
b. Infinite
c. R times the weight at the surface of Earth
d. 1 2R21 times the weight at the surface of Earth
Answer: a. Zero
Explanation: At the center of the Earth, the gravitational forces from all the surrounding mass cancel each other out, making the net gravitational force (and thus weight) zero.
7.) An apple falls on the surface of Earth due to its gravity. If the force exerted by Earth on the apple is 1F1 and the force by apple on Earth is 2F2, then
Options:
a. 1= 2F1=F2
b. 1≫ 2F1≫F2
c. 1> 2F1>F2
d. Can’t say
Answer: a. 1= 2F1=F2
Explanation: According to Newton’s third law, the force exerted by the Earth on the apple is equal and opposite to the force exerted by the apple on the Earth.
8.) Relative density of a substance depends on
Options:
a. Mass of substance
b. Volume of substance
c. Shape of substance
d. Material of substance
Answer: d. Material of substance
Explanation: Relative density is the ratio of the density of a substance to the density of a reference substance, usually water. It depends on the material of the substance, not its mass, volume, or shape.
9.) Relative density of mercury is 13.6. Its density is
Options:
a. 13.6 Kg/m313.6Kg/m3
b. 136 Kg/m3136Kg/m3
c. 1360 Kg/m31360Kg/m3
d. 13600 Kg/m313600Kg/m3
Answer: d. 13600 Kg/m313600Kg/m3
Explanation: The density of water is approximately 1000 Kg/m31000Kg/m3. The relative density of mercury is 13.6, so its density would be 13.6×1000=13600 Kg/m313.6×1000=13600Kg/m3.
10.) A boat having a length of 3 m3m and breadth of 2 m2m is floating on a lake. The boat sinks by 1 cm1cm when a man gets on it. The mass of the man is
Options:
a. 60 Kg60Kg
b. 72 Kg72Kg
c. 12 Kg12Kg
d. 128 Kg128Kg
Answer: b. 72 Kg72Kg
Explanation: The volume of water displaced is 3 m×2 m×0.01 m=0.06 m33m×2m×0.01m=0.06m3. The mass of the man would be 0.06 m3×1000 Kg/m3×9.8 m/s2=72 Kg0.06m3×1000Kg/m3×9.8m/s2=72Kg
1.) On which law Newton’s law of gravitation depends?
Answer: Newton’s law of gravitation is an independent law postulated by Newton and doesn’t “depend” on any other laws. It was formulated based on observations and is fundamental in the sense that it’s not derived from other laws.
2.) Which law can explain the falling of raindrop and snowfall?
Answer: The law of gravity explains the falling of raindrops and snowfall. Atmospheric conditions determine the form (raindrop or snowflake), but once formed, they fall to Earth due to gravitational attraction.
3.) Give SI unit of universal gravitation constant.
Answer: The SI unit of the universal gravitational constant G is N m2/kg2N m2/kg2 (Newton meter squared per kilogram squared).
4.) Which object falls to the earth at a faster rate, hollow or solid? Why?
Answer: In a vacuum, both hollow and solid objects will fall at the same rate due to gravity, irrespective of their mass. However, in the presence of air resistance, a solid object may fall faster because it is less affected by the drag forces, depending on the shape and material.
5.) Value of G on Earth is 6.67×10−11 N m2/kg26.67×10−11N m2/kg2. What is its value on the surface of the moon?
Answer: The universal gravitational constant G is a constant throughout the universe. Its value remains 6.67×10−11 N m2/kg26.67×10−11N m2/kg2 whether you are on the Earth, Moon, or anywhere else.
6.) State the factors on which the gravitational force between two objects depends.
Answer: The gravitational force between two objects depends on their masses and the distance between their centers. It is directly proportional to the product of their masses and inversely proportional to the square of the distance between them.
7.) Two bodies of masses 1m1 and 2m2 when separated by a distance d exert a force F on each other. What happens if the two objects are kept in water at the same distance?
Answer: If the two objects are kept in water at the same distance, the gravitational force between them remains the same, as it is not influenced by the medium. However, each object would experience an upward buoyant force due to the water.
8.) The weight of a bag of sugar at the equator is W. What happens to its weight at Antarctica? Why?
Answer: The weight of the bag of sugar will be slightly more at Antarctica compared to the equator. This is because the Earth is not a perfect sphere; it’s an oblate spheroid. As a result, gravitational pull is slightly stronger at the poles than at the equator.
9.) How do you measure mass and weight of an object?
Answer: Mass is usually measured with a balance, comparing it to known masses. Weight is the force exerted by gravity on the object and can be measured using a spring scale. The weight is related to the mass by Weight=mass×acceleration due to gravityWeight=mass×acceleration due to gravity.
10.) Which of the following remains constant during free falling?
Options:
i) Force
ii) Velocity
iii) Acceleration
iv) Momentum
Answer: iii) Acceleration
Explanation: During free fall, the only force acting on the object is gravity, which provides a constant acceleration towards the Earth’s center. The velocity changes due to this acceleration, and the force is a result of mass and acceleration, which are also changing.
1.) On the earth, a stone thrown horizontally from a point another stone is simultaneously dropped from the same point, Which stone would reach the ground first and why?
Answer: Both stones would reach the ground at the same time, assuming no air resistance. This is because the horizontal and vertical motions are independent of each other. Both stones are subject to the same acceleration due to gravity in the vertical direction.
12.) Suppose the gravity of Earth suddenly becomes zero, then what happens to the Moon if no other body affects it?
Answer: If the Earth’s gravity suddenly becomes zero, the Moon would continue in a straight line path at its current velocity because there would be no gravitational force to keep it in orbit around the Earth.
13.) What is the difference between g and G?
Answer: G is the Universal Gravitational Constant, a fundamental constant that describes the strength of gravity in the universe. g is the acceleration due to gravity at a specific location, like the surface of Earth. G is constant everywhere, while g can vary depending on where you are.
14.) Calculate average density of Earth in terms of g, G, and R-
Answer: The formula for the average density ρ of Earth in terms of g, G, and R (radius of Earth) is:
=3 4
ρ=4πGR3g
15.) A stone and a rubber ball of the same volume are kept on the surface of water. On which the buoyant force is more and why?
Answer: The buoyant force will be the same on both the stone and the rubber ball if they have the same volume. This is because buoyant force depends only on the volume of the fluid displaced, which is the same for both objects in this case.
16.) Two blocks, one of iron and the other of wood, are immersed in water at the same depth. Will both come upwards? Why?
Answer: The iron block will not come upwards because its density is greater than that of water. The wood block will come upwards because its density is less than that of water. Buoyant force depends on the volume and density of the fluid displaced, and it will not be enough to lift the iron block but will be sufficient for the wooden block.
17.) An object is immersed in different liquids. Is the same buoyant force acting on it? Why?
Answer: No, the buoyant force will differ depending on the density of the liquid in which the object is immersed. Buoyant force is proportional to the density of the fluid and the volume of fluid displaced, so changing the fluid will change the buoyant force.
18.) Why is a bucket of water lighter when in water than when it is taken out of water?
Answer: When the bucket is in water, it experiences a buoyant force that opposes the force of gravity, making it feel lighter. When taken out of water, the buoyant force is zero, so it feels heavier.
19.) Why are railway tracks laid on large-sized concrete sleepers? Explain
Answer: Railway tracks are laid on large-sized concrete sleepers to distribute the load of the train over a larger area. This reduces the pressure on the ground and prevents the tracks from sinking or deforming, ensuring a stable and smooth ride.
20.) A ship is loaded in sea water to maximum capacity. What will happen if the ship is moved to river water? Why?
Answer: The ship will sit lower in river water than in sea water. This is because sea water is denser than river water, providing more buoyancy. When the ship moves to river water, the reduced buoyancy may cause it to sink lower, possibly leading to the risk of it getting grounded if not managed carefully.
21.) When we jump into a swimming pool we feel lighter. Why?
Answer: We feel lighter because the buoyant force exerted by the water counteracts the force of gravity, reducing the effective weight we feel when submerged.
22.) If two equal weights of unequal volumes are balanced in air, what will happen when these are completely dipped in water?
Answer: If the two equal weights have unequal volumes, the one with the greater volume will displace more water when submerged, resulting in a greater buoyant force. Therefore, they will no longer be balanced when completely dipped in water.
23.) When an object is immersed in a liquid, what are the two forces that act on it? Explain with a diagram.
Answer: The two forces are the gravitational force (weight) acting downwards and the buoyant force acting upwards.
Diagram:
24.) If a body is compressed to half its previous volume, what will be the effect on its density and why?
Answer: If the body is compressed to half its previous volume, its density will double. This is because density is mass divided by volume ( = ρ=Vm), and if the volume is halved while the mass remains constant, the density will increase.
25.) A ball weighs 4Kg with a density of 4000Kg/m^3 is completely immersed in water of density 1000Kg/m^3. Find the buoyant force acting on it.
Answer: To find the buoyant force, we can use the formula for buoyancy:
= fluid× ×
Fb=ρfluid×V×g
First, we need to find the volume V of the ball, which can be calculated using:
= ball=4 Kg4000 Kg/m3=0.001 m3
V=ρballm=4000Kg/m34Kg=0.001m3
Then, the buoyant force Fb can be calculated as:
=1000 Kg/m3×0.001 m3×9.81 m/s2=9.81 N
Fb=1000Kg/m3×0.001m3×9.81m/s2=9.81N
The buoyant force acting on the ball is 9.81 N.
That covers all the remaining short answer questions. Would you like further clarification on any of these topics?