Class 9 Science – Chapter 10 Gravitation
Maximum Marks: 50 | Time: 1½ Hours
Section A – Multiple Choice Questions (1 × 5 = 5 marks)
(Each question carries 1 mark)
-
Which force is responsible for the moon revolving around the earth?
a) Centrifugal force
b) Centripetal force
c) Gravitational force
d) Frictional force -
The SI unit of Universal Gravitational Constant (G) is:
a) N m² kg⁻²
b) kg m/s²
c) J/kg
d) N/m -
The value of acceleration due to gravity (g) is maximum at:
a) Equator
b) Poles
c) Moon
d) Tropic of Cancer -
A cork floats on water because:
a) Its density is more than water
b) Its density is less than water
c) Its weight is more than buoyant force
d) None of these -
Pressure is defined as:
a) Force × Area
b) Force ÷ Area
c) Thrust × Volume
d) Weight ÷ Volume
Section B – Assertion & Reason (2 × 3 = 6 marks)
(Each question carries 2 marks. Choose the correct option.)
Options:
A. Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
B. Both Assertion and Reason are true, but Reason is not the correct explanation of Assertion.
C. Assertion is true, but Reason is false.
D. Assertion is false, but Reason is true.
-
Assertion (A): The weight of an object on the moon is less than its weight on the earth.
Reason (R): The gravitational force of the moon is one-sixth of that of the earth. -
Assertion (A): Free fall of an object means it falls without any resistance.
Reason (R): During free fall, only gravitational force acts on the object. -
Assertion (A): Sharp edges of nails help them to penetrate easily into the wall.
Reason (R): Pressure is directly proportional to the area of contact.
Section C – Short Answer Questions (3 × 5 = 15 marks)
(Each question carries 3 marks)
-
State the Universal Law of Gravitation and write its mathematical formula.
-
Differentiate between mass and weight (any three points).
-
Write the three equations of motion for a freely falling body.
-
Define buoyant force. On what two factors does it depend?
-
State Archimedes’ principle and give one application.
Section D – Long Answer Questions (4 × 6 = 24 marks)
(Each question carries 4 marks)
-
Derive the expression for acceleration due to gravity (g) at the surface of the Earth.
-
A ball is thrown upwards with an initial velocity of 20 m/s. Calculate:
a) The maximum height it will reach.
b) The total time taken to return to the ground.
(Take g = 10 m/s²) -
Why does a ship made of iron float on water while an iron nail sinks? Explain with Archimedes’ principle.
-
Write differences between thrust and pressure (at least four points). Give one example for each.
-
Define relative density. Why does a submarine sink when its buoyancy tanks are filled with water but rise when the tanks are emptied?
