# Physics MCQs Questions class 9 Force and laws of Motion with answers

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## Important points to remember about Force and laws of Motion

• motion of an object along a straight line in terms of its position, velocity and acceleration.
• We saw that such a motion can be uniform or non-uniform
• First law of motion: An object continues to be in a state of rest or of uniform motion along a straight line unless acted upon by an unbalanced force.
• The natural tendency of objects to resist a change in their state of rest or of uniform motion is called inertia.
•  The mass of an object is a measure of its inertia. Its SI unit is kilogram (kg).
• Force of friction always opposes motion of objects.
• Second law of motion: The rate of change of momentum of an object is proportional to the applied unbalanced force in the direction of the force.
•  The SI unit of force is kg m s–2. This is also known as newton and represented by the symbol N.
• A force of one newton produces an acceleration of 1 m s–2 on an object of mass 1 kg.
•  The momentum of an object is the product of its mass and velocity and has the same direction as that of the velocity. Its SI unit is kg m s–1
•  Third law of motion: To every action, there is an equal and opposite reaction and they act on two different bodies.
• In an isolated system (where there is no external force), the total momentum remains conserved.
• The law of conservation of momentum has been deduced from large number of observations and experiments.
•  This law was formulated nearly three centuries ago. It is interesting to note that not a single situation has been realised so far, which contradicts this law.
• Several experiences of every-day life can be explained on the basis of the law of conservation of momentum

## MCQs On Force and laws of Motion pdf

1. According to the third law of motion, action and reaction

(a) always act on the same body

(b) always act on different bodies in opposite directions

(c) have same magnitude and directions

(d) act on either body at normal to each other

2. The inertia of an object tends to cause the object_______

(a) to increase its speed

(b) to decrease its speed

(c) to resist any change in its state of motion

(d) to decelerate due to friction

3. An object of mass 2 kg is sliding with a constant velocity of 4 ms-1 on a frictionless horizontal table. The force required to keep the object moving with the same velocity is_______

(a) 32 N

(b) 0 N

(c) 2 N

(d) 8 N

4. Force is the rate of change of _______.

(a) momentum

(b) velocity

(c) displacement

(d) acceleration

5. The average force acted on the object is ______.

(a) 0.1 N

(b) 0.003 N

(c) 3.3 N

(d) 3 N

6. In SI system, the gravitational unit of force is ________.

(a) kg m s-2

(b) kgf

(c) m/s

(d) metre

7. Which one of the following is not a vector quantity?

(a) Speed

(b) Momentum

(c) Impulse

(d) Force

8. If the velocity-time graph representing the motion of a body is parallel to time-axis, then the net force acting on the body is _____

(a) 10 N

(b) 100 N

(c) 1 N

(d) None of these

9. Newton’s first law introduces the concept of________

(a) Momentum

(b) Inertia

(c) Conservation of energy.

(d) Action and reaction.

10. Momentum of the object is depend on.

(a) Mass

(b) Velocity

(c) Mass and velocity

(d) Force.

11. Quantitative expression of force is given by________

(a) Newton’s second law of motion.

(b) Newton’s third law of motion.

(c) Newton’s first law of motion.

(d) Newton’s law of gravitation.

12. The relation between acceleration, mass and force is given by_______

(a) a x F = m

(b) F = m/a

(c) F x m = a

(d) a = F/m

13. A man throws a ball weighing 200 g vertically upwards with a speed of 10m/s. Its momentum at the highest point of its flight will be_________

(a) 2 kg. m/s

(b) 2000 kg.m/s

(c) Insufficient data to find the momentum.

(d) zero.

14. A mass M breaks into two pieces in the ratio 1 : 3 while at rest. If the heavier has a speed of v, the speed of the lighter is__________

(a) v

(b) 2v

(c) 3v

(d) 4v

15. A carpenter exerts a force of magnitude 1.5 N at right angles to the surface of a nail of mass 3 gram to drive it into the wood. If wood offers a resistive force of 0.6 N and the time of interaction of hammer and the nail 0.01 s, the depth through which the nail penetrates is_______

(a) 15m

(b) 1.5 cm

(c) 15 cm

(d) 1.5 mm

16. A water tanker filled up to 2/3 of its height is moving with a uniform speed. On sudden application of the brake, the water in the tank would_________

(a) move backward

(b) move forward

(c) be unaffected

(d) rise upwards

17. A passenger in a moving train tosses a coin which falls behind him. It means that motion of the train is_______

(a) accelerated

(b) uniform

(c) retarded

(d) along circular tracks

18. Due to an acceleration of 2 m/s2, the velocity of a body increases from 20 m/s to 30 m/s in a certain period. Find the displacement (in m) of the body in that period.

(a) 650

(b) 125

(c) 250

(d) 325

19. Upon catching a ball, a cricket fielder swings his hands backwards. The concept behind this is explained by________

(a) Newton’s first law of motion

(b) Newton’s second law of motion

(c) Newton’s third law of motion

(d) The law of inertia