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

Q1: Who formulated the universal law of Gravitation?

Q2: What is free fall?

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

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

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

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

Answer: Gravitational force will double also.

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

Q6: How is gravity different from gravitation?

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

Q7: What is the 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 the symbol g.

Q8: Define the 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 the value of g the same on the earth and the moon?

Answer: The value of g varies from planet to planet. It has different values for the earth and the moon.

Q10: Why is the value of 'g; slightly higher at the 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, the value of g decreases.

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

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

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

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 the 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 sun's gravitation, even though it does not fall into the sun. Why?

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

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

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 the 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?

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

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

Answer: Mass is 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 to the ground first?

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

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

Answer: Because the value of acceleration due to gravity (g) at the moon's surface is nearly 1/6th of that at the surface of the 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 the gravitational constant (G)?