# Gravitation 1 - Mark Questions (Solved) CBSE Class 9 - Physics

**Q1: Who formulated the universal law of Gravitation?**

**Answer**: Isaac Newton

**Q2: What is free fall?**

**Answer**: When an object falls from any height under the influence of gravitational force only, it is known as free fall.

**Q3: What is the value of gravitational constant G on the earth? Does the value G changes on the moon?**

**Answer**: Value of gravitational constant on the earth is 6.67×10⁻¹¹ Nm²/kg². Value of G does not change (universal constant), it remains the same on moon.

**Q4: What will happen to gravitation force between two bodies, if mass of one body is doubled?**

**Answer**: Gravitational force will double also.

**Q5: Which force is responsible for the moon revolving round the earth?**

**Answer**: Gravitational force

**Q6: How is gravity different from gravitation?**

**Answer**: Gravitation is the force of attraction between any two bodies while gravity refers to attraction between any body and the earth.

**Q7: What is acceleration due to gravity?**

**Answer**: When an object falls towards the earth there is a change in its acceleration due to the gravitational force of the earth. So this acceleration is called acceleration due to gravity. It is denoted by symbol g.

**Q8: Define weight of a body. What is the SI unit of weight?**

**Answer**: The force with which the earth attracts a body towards its centre is called weight. The SI unit of weight is Newton (N). W = mg

**Q9: Is value of g same on the earth and the moon?**

**Answer**: Value of g varies planet to planet. It has different values for the earth and the moon.

**Q10: Why is value of 'g; slightly higher at poles (on the earth) than that of at the equator?**

**Answer**: As the radius of the earth increases from the poles to the equator, the value of g becomes greater at the poles than at the equator.

**Q11: As we go higher (at large heights), what happens to the value of g?**

**Answer**: As we go at large heights, value of g decreases.

**Q12: Name the scientist who gave the three laws of planetary motion.**

**Answer**: Johannes Kepler

**Q13: Which Kepler's law led Newton to establish inverse square rule in law of gravitation?**

**Answer**: Kepler's Third law i.e. T² ∝ r³

**Q14: What type of force is involved in the formation of tides in the sea?**

**Answer**: Gravitation force acted by the moon on the earth.

**Q15: What is the weight of a 1 kilogram mass on the earth? (g = 9.8 m/s²).**

**Answer**: W = mg = 1kg × 9.8m/s² = 9.8 N

**Q16: Is weight a force?**

**Answer**: Yes.

**Q17: When a body is dropped from a height, what is its initial velocity?**

**Answer**: Zero (0 m/s)

**Q18: On what factor/factors does the weight of a body depend?**

**Answer**: Since W = mg. It depends on

(i) mass of the object

(ii) value of 'g' on that planet.

**Q19: A body has a weight of 10 kg on the surface of earth. What will be its weight when taken to the centre of the earth?**

**Answer**: At the centre of the earth value of g = 0 m/s². Thus, weight = 0N

**Q20: The earth is acted upon the gravitation of the sun, even though it does not fall into the sun. Why?**

**Answer**: The gravitational force is responsible for providing the necessary centrepetal force. It allows the earth to revolve around the sun in defined circular orbit.

**Q21: The earth attracts the apple. Does the apple attract the earth also?**

**Answer**: Yes.

**Q22: Can gravitational force be repulsive?**

**Answer**: Never. It is always an attractive force.

**Q23: If the weight of a body on the earth is 6 N, what will it be on the moon?**

**Answer**: If the weight of a body on the earth is 6N, then its weight on the moon would be about 1N. This is because acceleration due to gravity on the surface of the moon is 1/6th the acceleration due to gravity on the earth’s surface.

**Q24: Is Newton's third law applicable to the gravitational force?**

**Answer**: Yes.

**Q25: If a stone is thrown upwards, while calculating the maximum height it reaches, acceleration due to gravity is taken as positive or negative value?**

**Answer**: Negative value

**Q26: Which is more fundamental, the mass of a body or its weight? Why?**

**Answer**: Mass is more fundamental because it remains constant at all places, irrespective of a change in place. But weight depends on acceleration due to gravity g, which varies with location.

**Q27: Two stones of mass 1kg and 10kg are dropped simultaneously from the top of a tower of 100m. Assuming negligible air resistance, which stone will react the ground first?**

**Answer**: Both will reach ground at the same time.

**Q28: Why one can jump higher on the surface of moon than on the earth ?**

**Answer**: Because the value of acceleration due to gravity (g) at moon surface is nearly 1/6th of that at the surface of earth.

**Q29: What kind of quantity is weight – a scalar or a vector?**

**Answer**: Weight is a vector quantity.

**Q30: Who found out the value of gravitational constant (G)?**

**Answer**: Henry Cavendish.

**👉See Also:**

Ch 10 - Gravitation (Worksheet-1)

Ch 10 - Gravitation (Q & A, Study Notes, NCERT Solution)

Ch10 - Gravitation (MCQs)

Ch 10 - Gravitation (Understanding Mass and Weight)

Ch 10 - Gravitation - 51 Question You must Revise

Ch 10 - Gravitation (Worksheet-2)

Ch 10 - Gravitation and Flotation (Solved Problems)

Ch 10 - Gravitation (Q & A, Study Notes, NCERT Solution)

Ch10 - Gravitation (MCQs)

Ch 10 - Gravitation (Understanding Mass and Weight)

Ch 10 - Gravitation - 51 Question You must Revise

Ch 10 - Gravitation (Worksheet-2)

Ch 10 - Gravitation and Flotation (Solved Problems)

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