Class 9 Physics Unit-3: Dynamics, Solved MCQs With Verified Answers. (Sindh Textbook Board, Jamshoro)

1. Newton's First law of motion is also known as the law of scale

(a) speed
(b) rest
(c) inertia
(d) force

... Answer is (c) inertia
Inertia is the property of an object due to which it tends to continue its state of rest or motion. Inertia is resistance to change the state.

2. Quantity of matter contained in the body is called

(a) mass
(b) volume
(c) area
(d) weight

... Answer is (a) mass
Definition of Mass

3. Quantity of motion contained in a body is called

(a) force
(b) inertia
(c) momentum
(d) gravity

... Answer is (c) momentum
p = mv

4. Law of conservation of momentum defines the total momentum of a system of two bodies before and after collision

(a) remains constant
(b) retains more momentum
(c) losses some momentum
(d) None of the above is true

... Answer is (a) remains constant
Statement of Law of conservation of momentum

5. Weight of a body can be measured using a spring balance, it differs from place to place because of variations in

(a) acceleration
(b) gravitational pull
(c) velocity
(d) size of spring balance

... Answer is (c) gravitational pull
Weight w = mg, where g is acceleration due gravity = GM/R2

6. It is easier to push an empty shopping cart than a full one because the filled cart has more mass than the empty one. This can be expressed by

(a) F > m
(b) F < m
(c) F ∝ 1/m
(d) F ∝ m

... Answer is (d) F ∝ m
Newton's 2nd law of motion

7. Centrifugal force is always directed :

(a) towards centre
(b) away from centre
(c) along the circular path
(d) all sides

... Answer is (b) away from the centre
Centrifugal force is always directed away from the centre, while Centripetal force is always directed towards the centre

8. Friction opposes motion between two bodies in contact because of

(a) charges on bodies
(b) weight of bodies
(c) roughness of surfaces
(d) None of above

... Answer is (c) the roughness of surfaces
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9. Which statement is true for limiting frictional force.

(a) it is greater than rolling friction
(b) it is greater than sliding friction
(c) it is greater than kinetic friction
(d) all are true

... Answer is (d) all are true
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10. A man pulls a crate of mass 25 kg across the levelled ground with a horizontal force of 60 N.A constant force of friction of 20 N acts on the sledge. What is the acceleration of the sledge?

(a) 0.63 m s⁻¹
(b) 1.6 m s⁻¹
(c) 2.4 m s⁻¹
(d) 3.2m s⁻¹

... Answer is (b) 1.6 m s⁻¹
Net force acting on the sledge = 60 N - 20 N = 40 N, From Newton's 2nd Law F = ma, a = F/m = 40 N/25 kg = 1.6 m s⁻¹

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