## Gravitation - 51 Questions You must revise

**Q1**: What was geocentric model? Who proposed this theory?

**Q2**: What was heliocentric theory? Who proposed this?

**Q3**: If the mass of the body is 9.8 kg on the earth what would be its mass on the moon.

**Q4**: What are the Kepler Laws that govern the motion of the planets?

**Q5(NCERT/CBSE 2010)**: State the universal law of gravitation.

**Q6(NCERT)**: What is the importance of Universal Law of Gravitation?

or

**Q(CBSE 2010)**: State any one phenomena related to the Universal Law of Gravitation.

**Q7(CBSE 2010)**: Why is G called the Universal Constant?

**Q8**: Who measured the value of G first time, experimentally?

**Q9(CBSE 2010/NCERT)**: What is the gravitational force between the Earth and a body called? In which direction does it occur?

**Q10**: An object moves in a circular motion due to centripetal force, acting towards the center. The moon also rotates around the earth? Does centripetal force acts on it? Why does the moon not fall on the earth?

or

**Q(NCERT)**:If the moon attracts the earth, why does the earth not move towards the moon?

**Q11**: 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?

**Q12**: How gravitational force is different from or similar to magnetic force (between two magnets) or coulomb force (between two charged object)?

**Q13(NCERT)**: Calculate the force of gravitation between the earth and the Sun, given that the mass of the earth = 6 × 10²⁴ kg and of the Sun = 2 × 10³⁰ kg. The average distance between the two is 1.5 × 10ⁱⁱ m.

**Q14(CBSE 2010)**: The Earth attracts an apple. Does the apple also attract the Earth? If it does, why does the Earth not move towards the apple?

**Q15(CBSE 2010)**: How is gravitational force of attraction between two bodies affected if

(i) Mass of both bodies is doubled.

(ii) Distance between them is halved.

**Q16(NCERT/CBSE 2011)**: What happens to the force between two objects, if

(i) the mass of one object is doubled?

(ii) the distance between the objects is doubled and tripled?

(iii) the masses of both objects are doubled?

**Q17**: 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.

**Q18**: Does the force of attraction between two objects depend on the properties of intervening medium?

**Q19**: Does Law of gravitation obey Newton's third law of motion?

**Q20(NCERT)**: What is free fall?

**Q21**: Define 'g' or acceleration due to gravity? Does it depend on the mass of the body (near the surface of the earth)experiencing 'g'?

**Q22**: (a)(CBSE 2011) 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.

**Q23**: How does value of 'g' vary on the earth? What are the factors responsible for this?

**Q24**: What happens to 'g' experienced by a body when it moves up the earth's surface?

**Q25**: 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.

**Q26(NCERT)**: Why is the weight of an object on the moon 1/6th its weight on the earth?

**Q27(NCERT)**: Gravitational force acts on all objects in proportion to their masses. Why then, a heavy object does not fall faster than a light object?

**Q28(NCERT)**: What is the magnitude of the gravitational force between the earth and a 1 kg object on its surface? (Mass of the earth is 6 × 10²⁴ kg and radius of the earth is 6.4 × 10⁶ m).

**Q29**: Define mass.

**Q30(CBSE 2010)**: Define weight? How it is related to mass?

**Q31(CBSE 2010)**: Mass of an object is 10 kg. What is its weight on the Earth? (g = 9.8 m/s².)

**Q32(NCERT/CBSE 2011)**: What are the differences between the mass of an object and its weight?

**Q33**: Why the value of g is greater at the poles than at the equator?

**Q34(NCERT)**: Amit buys few grams of gold at the poles as per the instruction of one of his friends. He hands over the same when he meets him at the equator. Will the friend agree with the weight of gold bought? If not, why? [Hint: The value of g is greater at the poles than at the equator].

**Q35(NCERT)**: Gravitational force on the surface of the moon is only 1/6th as strong as gravitational force on the Earth. What is the weight in newtons of a 10 kg object on the moon and on the Earth? What is the value of 'g' at the surface of the moon?

**Q36(CBSE 2010)**: Write the standard equations of motion when an object is thrown upwards with some initial velocity?

**Q37**: Write the standard equations in the form when an object is dropped from a height?

**Q38**: Is acceleration due to gravity a vector or a scalar? Write its S.I. unit.

**Q39(NCERT)**: 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.

**Q40(NCERT)**: A stone is released from the top of a tower of height 19.6 m. Calculate its final velocity just before touching the ground.

**Q41(NCERT)**: A stone is thrown vertically upward with an initial velocity of 40 m/s. Taking g = 10 m/s², find the maximum height reached by the stone. What is the net displacement and the total distance covered by the stone?

**Q42(NCERT)**: 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.

**Q43**: A ball is thrown upwards from the ground of a tower with a speed of 20 m/s. There is a window in the tower at the height of 15m from ground. How many times and when will the ball pass the window? (g = 10 m/s²)

**Q44**: 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?

**Q45**: A ball is thrown with some velocity 'u' m/s. Show that under free fall, it will fall the ground with same velocity.

**Q46**: Why will a sheet paper fall slower than one that is crumpled into a ball?

**Q47**: Two stones A and B are dropped from a multi-storied 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/s²).

**Q48**: Which force bring tides in the ocean?

**Q49**: In vacuum, which of the two a feather and a coin reach the ground first on being dropped?

**Q50**: The astronauts in space feel weightless. Why?

**Q51**: Shikha buys a few grams of precious stones in Delhi. She takes them to equator and is surprised to see that their weight is reduced. She thinks that she has been cheated. She goes back to the seller and claims the exchange amount. The shopkeeper explains her how weight differs due to value of g. Satisfied, Shikha goes back.

Read the above passage and answer the following questions:

(i) List few values of Shikha.

(ii) What are the values of shopkeeper?

(iii) How does g vary with distances?

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