In this blogpost we will discuss MCQs on Unit 3: Laws of Motion
1. Newton’s First Law of Motion states that an object at rest will remain at rest unless?
A) A force acts on it
B) A balanced force acts on it
C) An unbalanced force acts on it
D) There is no friction
Answer: C) An unbalanced force acts on it
Explanation: Newton’s First Law of Motion, also known as the law of inertia, states that an object will stay at rest or continue moving with constant velocity unless acted upon by an unbalanced force.
2. The rate of change of momentum is?
A) Force
B) Velocity
C) Acceleration
D) Impulse
Answer: A) Force
Explanation: According to Newton’s Second Law of Motion, the rate of change of momentum is equal to the force applied to an object. Mathematically, F=dpdtF = \frac{dp}{dt}F=dtdp.
3. Newton’s Third Law of Motion states that?
A) Every object in motion stays in motion
B) For every action, there is an equal and opposite reaction
C) Force is equal to mass times acceleration
D) Objects at rest remain at rest unless acted upon by a force
Answer: B) For every action, there is an equal and opposite reaction
Explanation: Newton’s Third Law of Motion states that any force exerted on a body will create a force of equal magnitude in the opposite direction.
4. An object experiences a force of 10 N. If the object’s mass is 2 kg, what is its acceleration?
A) 2 m/s²
B) 5 m/s²
C) 10 m/s²
D) 20 m/s²
Answer: B) 5 m/s²
Explanation: Using Newton’s Second Law, F=maF = maF=ma, rearranged to a=Fma = \frac{F}{m}a=mF. So, a=102=5 m/s2a = \frac{10}{2} = 5 \, \text{m/s}^2a=210=5m/s2.
5. Which of the following best explains inertia?
A) An object will keep moving unless stopped by friction.
B) A body will remain at rest unless acted upon by an external force.
C) A body will change its velocity only when a net force is applied.
D) A body will accelerate when acted upon by a force.
Answer: B) A body will remain at rest unless acted upon by an external force.
Explanation: Inertia is the tendency of an object to resist changes in its state of motion, whether it is at rest or in motion.
6. The force acting on a body of mass 5 kg gives an acceleration of 2 m/s². What is the force?
A) 2 N
B) 5 N
C) 7 N
D) 10 N
Answer: D) 10 N
Explanation: Using F=maF = maF=ma, F=5×2=10 NF = 5 \times 2 = 10 \, \text{N}F=5×2=10N.
7. What is the SI unit of force?
A) Newton
B) Joule
C) Meter
D) Kilogram
Answer: A) Newton
Explanation: The SI unit of force is the Newton (N), which is defined as the force required to accelerate a 1 kg mass by 1 m/s².
8. The weight of an object is?
A) Mass
B) Gravitational force acting on the object
C) Its inertia
D) The same as its mass
Answer: B) Gravitational force acting on the object
Explanation: The weight of an object is the force with which it is pulled towards the Earth due to gravity, W=mgW = mgW=mg, where mmm is mass and ggg is the acceleration due to gravity.
9. The force required to keep an object moving with uniform velocity is?
A) Equal to the gravitational force
B) Equal to the applied force
C) Zero
D) Equal to the frictional force
Answer: D) Equal to the frictional force
Explanation: To maintain uniform velocity, the applied force must exactly counteract any frictional forces acting on the object.
10. The momentum of an object is defined as?
A) The mass of the object multiplied by its velocity
B) The mass of the object divided by its velocity
C) The force acting on the object multiplied by its time
D) The change in the velocity of the object
Answer: A) The mass of the object multiplied by its velocity
Explanation: Momentum is defined as p=mvp = mvp=mv, where mmm is mass and vvv is velocity.
11. If the force acting on an object is doubled, its acceleration will?
A) Stay the same
B) Double
C) Increase four times
D) Be halved
Answer: B) Double
Explanation: From Newton’s Second Law F=maF = maF=ma, if the force is doubled and mass remains constant, the acceleration will also double.
12. An object is moving in a circular path with uniform speed. The force responsible for the change in direction of the object is?
A) Centripetal force
B) Frictional force
C) Gravitational force
D) Centrifugal force
Answer: A) Centripetal force
Explanation: Centripetal force is the force that acts towards the center of the circular path, keeping the object in uniform circular motion.
13. The law of inertia is a consequence of?
A) Newton’s First Law
B) Newton’s Second Law
C) Newton’s Third Law
D) Law of Gravitation
Answer: A) Newton’s First Law
Explanation: The law of inertia is a direct consequence of Newton’s First Law, which states that an object at rest stays at rest unless acted upon by an external force.
14. An object of mass 10 kg is subjected to a force of 50 N. What is its acceleration?
A) 2 m/s²
B) 5 m/s²
C) 10 m/s²
D) 50 m/s²
Answer: B) 5 m/s²
Explanation: Using F=maF = maF=ma, we get a=Fm=5010=5 m/s2a = \frac{F}{m} = \frac{50}{10} = 5 \, \text{m/s}^2a=mF=1050=5m/s2.
15. A rocket moves upwards due to the force exerted by the exhaust gases. This is an example of which law?
A) Newton’s First Law
B) Newton’s Second Law
C) Newton’s Third Law
D) Law of Universal Gravitation
Answer: C) Newton’s Third Law
Explanation: According to Newton’s Third Law, the rocket moves upwards because the exhaust gases exert a downward force, and the rocket experiences an equal and opposite upward force.
16. If two forces act on an object in opposite directions, the net force is?
A) The sum of the forces
B) The difference between the forces
C) Zero
D) Equal to the larger force
Answer: B) The difference between the forces
Explanation: When two forces act in opposite directions, the net force is the difference between the magnitudes of the two forces.
17. A person is standing in an elevator that is moving upwards with acceleration. The force that the person exerts on the floor is?
A) Equal to their weight
B) Greater than their weight
C) Less than their weight
D) Zero
Answer: B) Greater than their weight
Explanation: When the elevator is accelerating upwards, the person experiences an increased apparent weight due to the additional force needed to accelerate.
18. The frictional force between two surfaces depends on?
A) The speed of motion
B) The area of contact
C) The nature of the surfaces in contact
D) The shape of the object
Answer: C) The nature of the surfaces in contact
Explanation: The amount of friction depends on the roughness of the surfaces and the force pressing them together, not the area of contact.
19. What is the direction of the frictional force when an object is sliding on a surface?
A) In the direction of motion
B) Opposite to the direction of motion
C) Perpendicular to the motion
D) No friction acts
Answer: B) Opposite to the direction of motion
Explanation: Friction always opposes the relative motion between two surfaces.
20. If the mass of an object is doubled, what happens to its momentum when the velocity remains constant?
A) The momentum doubles
B) The momentum is halved
C) The momentum remains the same
D) The momentum quadruples
Answer: A) The momentum doubles
Explanation: Momentum is directly proportional to mass, so if the mass is doubled, the momentum will also double.
21. The force required to maintain a body in uniform circular motion is called?
A) Centripetal force
B) Gravitational force
C) Tension
D) Frictional force
Answer: A) Centripetal force
Explanation: Centripetal force is the force that acts towards the center of the circular path to keep the object in motion.
22. When a bullet is fired from a gun, the gun experiences a recoil. This is an example of?
A) Newton’s First Law
B) Newton’s Second Law
C) Newton’s Third Law
D) Law of Conservation of Momentum
Answer: C) Newton’s Third Law
Explanation: The gun’s recoil is a reaction to the bullet being fired, as stated by Newton’s Third Law: for every action, there is an equal and opposite reaction.
23. The force of friction depends on?
A) Speed of the object
B) The type of material
C) The weight of the object
D) All of the above
Answer: D) All of the above
Explanation: Friction depends on the nature of the materials in contact, the weight of the object, and in some cases, the speed of the object.
24. If two objects of different masses fall freely under gravity, which will reach the ground first?
A) The object with more mass
B) The object with less mass
C) Both will reach the ground at the same time
D) It depends on the shape of the object
Answer: C) Both will reach the ground at the same time
Explanation: In the absence of air resistance, all objects fall with the same acceleration due to gravity, regardless of their mass.
25. The SI unit of momentum is?
A) kg
B) m/s
C) N·s
D) kg·m/s
Answer: D) kg·m/s
Explanation: Momentum is the product of mass and velocity, so its SI unit is kg⋅m/s\text{kg} \cdot \text{m/s}kg⋅m/s.
26. The frictional force acting on an object depends on which of the following?
A) Speed of the object
B) Surface area in contact
C) Normal force
D) All of the above
Answer: C) Normal force
Explanation: The frictional force is directly proportional to the normal force, which is the force exerted by a surface perpendicular to the object.
27. Which of the following is true for an object in free fall?
A) It experiences no force.
B) It accelerates at a constant rate due to gravity.
C) It moves in a straight line with constant velocity.
D) Its acceleration increases as it falls.
Answer: B) It accelerates at a constant rate due to gravity.
Explanation: When an object is in free fall, it accelerates downwards at a constant rate, which is approximately 9.8 m/s29.8 \, \text{m/s}^29.8m/s2 on Earth, due to the force of gravity.
28. An object is in motion under the action of a constant force. According to Newton’s Second Law, the acceleration is?
A) Inversely proportional to the mass of the object.
B) Directly proportional to the mass of the object.
C) Inversely proportional to the applied force.
D) Directly proportional to the applied force.
Answer: D) Directly proportional to the applied force.
Explanation: According to Newton’s Second Law, F=maF = maF=ma, acceleration is directly proportional to the applied force and inversely proportional to the object’s mass.
29. The unit of work in the SI system is?
A) Joule
B) Newton
C) Watt
D) Meter
Answer: A) Joule
Explanation: The SI unit of work is the Joule (J), which is defined as the amount of work done when a force of 1 newton is applied over a distance of 1 meter.
30. If a body moves in a circle with constant speed, the force acting on it is?
A) Zero
B) Constant and directed radially outward
C) Constant and directed radially inward
D) Varying in magnitude and direction
Answer: C) Constant and directed radially inward
Explanation: When a body moves in a circle with constant speed, the force acting on it is centripetal force, which is always directed radially inward toward the center of the circle.
31. The reaction force for a car moving forward is?
A) The engine pushing the car forward.
B) The road pushing the tires upward.
C) The friction between the tires and the road.
D) The car pushing the road backward.
Answer: D) The car pushing the road backward.
Explanation: According to Newton’s Third Law, the reaction force to the car moving forward is the force exerted by the car on the road, pushing the road backward.
32. A person standing in an elevator that is accelerating downward will feel?
A) A normal force equal to their weight.
B) A normal force greater than their weight.
C) A normal force less than their weight.
D) No normal force.
Answer: C) A normal force less than their weight.
Explanation: When the elevator accelerates downward, the person feels lighter because the normal force exerted by the floor is less than their actual weight.
33. The action and reaction forces are always?
A) Equal in magnitude and opposite in direction, but act on the same body.
B) Equal in magnitude and opposite in direction, and act on different bodies.
C) Unequal and opposite in direction.
D) Equal in magnitude, but do not act on different bodies.
Answer: B) Equal in magnitude and opposite in direction, and act on different bodies.
Explanation: Newton’s Third Law states that action and reaction forces are equal in magnitude and opposite in direction, but they act on different bodies.
34. A car travels with a constant speed around a circular track. The work done by the centripetal force is?
A) Positive
B) Negative
C) Zero
D) Undefined
Answer: C) Zero
Explanation: The centripetal force does no work because it is always perpendicular to the direction of motion of the car. Work is only done when a force has a component in the direction of displacement.
35. Which of the following statements is true about the frictional force acting on an object?
A) It is independent of the surface area in contact.
B) It is directly proportional to the surface area in contact.
C) It is independent of the normal force.
D) It depends on the nature of the surfaces in contact.
Answer: D) It depends on the nature of the surfaces in contact.
Explanation: Friction depends on the roughness of the surfaces in contact and the force pressing them together (normal force), not on the surface area.
36. If an object is moving with a constant velocity, the net force acting on it is?
A) Zero
B) Equal to its weight
C) Equal to its mass times acceleration
D) None of the above
Answer: A) Zero
Explanation: According to Newton’s First Law, if an object is moving with a constant velocity, the net force acting on it must be zero, meaning there is no unbalanced force.
37. The momentum of a body of mass mmm moving with velocity vvv is given by?
A) mv2mv^2mv2
B) m/vm/vm/v
C) mvmvmv
D) m/v2m/v^2m/v2
Answer: C) mvmvmv
Explanation: The momentum of an object is given by the product of its mass and velocity, p=mvp = mvp=mv.
38. An object is moving in a straight line with constant velocity. What is its acceleration?
A) Positive
B) Zero
C) Negative
D) Constant
Answer: B) Zero
Explanation: If an object is moving with constant velocity, its acceleration is zero because there is no change in its speed or direction.
39. The frictional force between two surfaces depends on the?
A) Speed of the object.
B) Area of contact.
C) Weight of the object.
D) None of the above.
Answer: C) Weight of the object.
Explanation: The frictional force is proportional to the normal force (which is often equal to the weight of the object), and the nature of the surfaces in contact.
40. Which of the following is true about static friction?
A) It is independent of the weight of the object.
B) It can vary depending on the applied force.
C) It is constant at all times.
D) It is zero when the object is at rest.
Answer: B) It can vary depending on the applied force.
Explanation: Static friction adjusts itself to match the applied force up to a maximum limit, beyond which the object starts to move and kinetic friction takes over.
41. The acceleration due to gravity on the surface of the Earth is approximately?
A) 9.8 m/s29.8 \, \text{m/s}^29.8m/s2
B) 10 m/s210 \, \text{m/s}^210m/s2
C) 9.8 km/s29.8 \, \text{km/s}^29.8km/s2
D) 1 m/s21 \, \text{m/s}^21m/s2
Answer: A) 9.8 m/s29.8 \, \text{m/s}^29.8m/s2
Explanation: The acceleration due to gravity near the Earth’s surface is approximately 9.8 m/s29.8 \, \text{m/s}^29.8m/s2.
42. When a car suddenly stops, the passengers are thrown forward due to?
A) Inertia
B) Centripetal force
C) Newton’s First Law
D) Gravitational force
Answer: A) Inertia
Explanation: The passengers continue moving forward due to their inertia, which causes them to resist changes in their state of motion.
43. If a body is acted upon by a net force, what will happen to its velocity?
A) It will decrease
B) It will remain constant
C) It will increase or change direction
D) It will become zero
Answer: C) It will increase or change direction
Explanation: According to Newton’s Second Law, when a net force acts on a body, it will cause a change in velocity, either by increasing it or by changing its direction.
44. A body is moving under the influence of two forces, F1F_1F1 and F2F_2F2. The net force acting on the body is?
A) F1+F2F_1 + F_2F1+F2
B) F1−F2F_1 – F_2F1−F2
C) F1×F2F_1 \times F_2F1×F2
D) The vector sum of F1F_1F1 and F2F_2F2
Answer: D) The vector sum of F1F_1F1 and F2F_2F2
Explanation: The net force acting on an object is the vector sum of all the individual forces acting on it.
45. The frictional force that resists the motion of a body depends on the?
A) Velocity of the body
B) Area of contact
C) Weight of the body
D) Shape of the body
Answer: C) Weight of the body
Explanation: The frictional force is proportional to the normal force, which is often equal to the weight of the body.
46. If the mass of an object is halved while the velocity remains constant, its momentum will?
A) Double
B) Stay the same
C) Half
D) Increase four times
Answer: C) Half
Explanation: Momentum is directly proportional to mass. If mass is halved, momentum will also be halved.
47. A stone is thrown vertically upward. At the highest point, its velocity is?
A) Maximum
B) Zero
C) Negative
D) None of the above
Answer: B) Zero
Explanation: At the highest point of a projectile’s motion, the vertical velocity becomes zero before it starts coming back down.
48. The weight of an object at the center of the Earth is?
A) Maximum
B) Zero
C) Half its weight at the surface
D) Infinity
Answer: B) Zero
Explanation: At the center of the Earth, the gravitational forces from all directions cancel out, making the weight zero.
49. A body is moving with a constant velocity of 10 m/s. The force acting on it is?
A) Zero
B) 10 N
C) 100 N
D) Varies with time
Answer: A) Zero
Explanation: A body moving with constant velocity experiences no net force according to Newton’s First Law.
50. Which of the following is true about Newton’s Laws of Motion?
A) They only apply to objects in motion.
B) They only apply to objects at rest.
C) They apply to both objects at rest and in motion.
D) They apply only in outer space.
Answer: C) They apply to both objects at rest and in motion.
Explanation: Newton’s Laws of Motion apply to both objects at rest and in motion. They describe how forces affect the motion (or lack of motion) of objects.
These 50 MCQs on Laws of Motion are designed to test your understanding of Newton’s Three Laws of Motion, momentum, force, and friction. By reviewing the answers and explanations, you can reinforce your knowledge and prepare for exams effectively. Continue practicing to deepen your understanding of the fundamental concepts in classical mechanics!
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