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Q1. A rocket expels hot gases downward to propel itself upward. This is a direct application of:
A rocket works on the principle of Newton’s Third Law. The hot gases expelled downward are the action force, and the rocket moving upward is the reaction force. This is the same principle that explains recoil.
Q2. When you are standing on a skateboard and throw a heavy ball forward, what happens to you and the skateboard?
According to Newton’s Third Law, when you throw the ball forward (action), the ball exerts an equal and opposite force on you, causing you and the skateboard to move backward (reaction).
Q3. A large truck and a small car have a head-on collision. Which vehicle experiences the greater force during the impact?
According to Newton’s Third Law, the force exerted by the truck on the car is equal in magnitude to the force exerted by the car on the truck. The forces are equal and opposite regardless of their masses.
Q4. What is the net force acting on a book resting on a table?
The book is at rest, so the forces acting on it are balanced. The downward weight is balanced by the upward normal force from the table, resulting in a net force of zero.
Q5. An object has a mass of 10 kg. What is its weight on Earth? (Take g ≈ 10 m/s²)
Weight = mass × acceleration due to gravity = m × g = 10 kg × 10 m/s² = 100 N.
Q6. If you push on a heavy crate and it doesn’t move, what can you say about the forces acting on it?
Static friction adjusts itself to oppose the applied force up to a maximum value. If the crate doesn’t move, the applied push is less than or equal to the maximum static friction.
Q7. A force of 20 N accelerates a 5 kg object. What is the object’s acceleration?
Using Newton’s Second Law, a = F/m = 20 N / 5 kg = 4 m/s².
Q8. Which of the following best describes the property of “inertia”?
Inertia is the inherent property of an object to resist any change in its state of rest or uniform motion. It is not a force but a property of matter.
Q9. In a vacuum on the Moon, where there is no air, a feather and a hammer dropped from the same height will:
In the absence of air resistance, all objects fall with the same acceleration due to gravity regardless of their mass. This was famously demonstrated by Galileo and later on the Moon by astronaut David Scott.
Q10. The impulse experienced by an object is equal to:
Impulse is defined as force × time, and it is equal to the change in momentum of the object (Impulse = Δp = F × t).
Q11. Conservation laws such as momentum and energy are:
Conservation laws are not just mathematical proofs but are based on experimental observations and have been tested extensively. They are fundamental principles of physics.
Q12. A single experiment that disagrees with a conservation law can:
In science, a single reproducible experiment that contradicts a law can disprove it. Conservation laws are well-established because no such experiment has been found.
Q13. The law of conservation of momentum is:
The law of conservation of momentum was formulated by Newton in the 17th century, making it around three centuries old.
Q14. Conservation of momentum applies when:
The law of conservation of momentum applies only when no external unbalanced force acts on the system. Only internal forces act between the objects in the system.
Q15. The first law of motion states that an object remains in motion unless:
Newton’s First Law states that an object continues in its state of rest or uniform motion unless acted upon by an unbalanced external force.
Q16. The natural tendency of objects to resist change in motion is:
Inertia is the natural tendency of objects to resist changes in their state of motion. It is the fundamental concept behind Newton’s First Law.
Q17. The measure of inertia is:
Mass is the quantitative measure of inertia. Greater mass means greater inertia, meaning it is harder to change the object’s state of motion.
Q18. The SI unit of mass is:
The SI unit of mass is the kilogram (kg). Newton is the unit of force, Joule is the unit of energy, and Watt is the unit of power.
Q19. Force of friction always:
Friction always opposes relative motion or the tendency of relative motion between two surfaces in contact. It acts in the direction opposite to motion.
Q20. Second law relates force to:
Newton’s Second Law states that the net force acting on an object is equal to the rate of change of its momentum. F = dp/dt.
Q21. SI unit of force is:
The SI unit of force is the newton (N), named after Sir Isaac Newton. 1 N = 1 kg·m/s².
Q22. Momentum equals:
Momentum (p) is defined as the product of mass (m) and velocity (v). p = m × v.
Q23. Momentum has the same direction as:
Momentum is a vector quantity and its direction is the same as the direction of velocity, since momentum = mass × velocity and mass is a scalar.
Q24. Third law states that action and reaction:
Newton’s Third Law states that for every action, there is an equal and opposite reaction. These forces act on different bodies.
Q25. A person pushes against a solid wall, but the wall doesn’t move. Why does the person not fall over backwards?
When a person pushes against a wall, the wall pushes back. The person doesn’t fall because the friction between the shoes and the floor provides an equal and opposite horizontal force, balancing the reaction from the wall.
Q26. If you drop your pencil while inside a moving train that is going at a constant speed, where will the pencil land relative to your hand?
The pencil has the same horizontal velocity as the train and your hand. So when dropped, it falls straight down relative to you and lands directly below your hand.
Q27. Two objects after collision move with new velocities because:
During a collision, the total momentum is conserved. The objects exchange momentum, resulting in new velocities after the collision.
Q28. When carpet is beaten, dust comes out due to:
When the carpet is beaten, the carpet moves but the dust particles tend to remain at rest due to their inertia. This causes the dust to separate from the carpet.
Q29. Luggage on a bus roof must be tied because:
When the bus stops or turns suddenly, the luggage tends to continue moving due to its inertia. Tying it prevents it from falling off.
Q30. A ball slows down on the ground because of:
When a ball rolls on the ground, the force of friction acts opposite to its motion, causing it to slow down and eventually stop.
Q31. An object with net zero force can still move at:
According to Newton’s First Law, if the net force is zero, the object will continue moving with constant velocity (or remain at rest).
Q32. A truck rolling down a hill with constant acceleration obeys:
Constant acceleration means the net force is constant (F = ma). This is described by Newton’s Second Law of Motion.
Q33. Force needed to stop a vehicle depends on:
The force needed to stop a vehicle depends on its mass and the acceleration (deceleration) required to bring it to rest. This is given by F = ma.
Q34. Friction on a stone sliding on ice causes:
Friction acts opposite to the motion of the stone, causing it to slow down. This negative acceleration is called deceleration.
Q35. A cabinet moving at constant velocity under applied force implies:
For constant velocity, acceleration is zero, so the net force is zero. This means the applied force is balanced by the frictional force.
Q36. In a train pulled by an engine, friction of track acts:
Friction between the train wheels and the track opposes the motion of the train, so it acts in the backward direction.
Q37. If engine force > friction force, train will:
If the engine force is greater than the friction force, there is a net forward force, causing the train to accelerate in the forward direction.
Q38. Momentum of an object is:
Momentum (p) is the product of mass (m) and velocity (v): p = mv.
Q39. When two objects move in opposite directions, total momentum is:
Since momentum is a vector, when objects move in opposite directions, their momenta have opposite signs. The total momentum is the algebraic sum, which is the difference of their magnitudes.
Q40. Opposite direction motion is represented using:
To represent opposite directions, we assign positive sign to one direction and negative sign to the opposite direction. This allows us to add momenta algebraically.
Q41. Law of conservation of momentum has:
The law of conservation of momentum is one of the most well-established laws in physics. No experimental contradiction has been found so far.
Q42. Force of friction acts:
Friction always opposes relative motion or the tendency of relative motion between surfaces in contact.
Q43. A net zero unbalanced force gives:
When the net force is zero, acceleration is zero, so the object moves with constant velocity (Newton’s First Law).
Q44. When two masses collide and stick together, the collision is:
When objects stick together after collision, it is called a perfectly inelastic collision. Kinetic energy is not conserved, though momentum is conserved.
Q45. When truck rolls downhill, its acceleration is:
On a uniform slope with constant gravitational force and ignoring air resistance, the truck experiences constant acceleration due to gravity.
Q46. Higher mass means:
Mass is the measure of inertia. Higher mass means greater resistance to changes in motion, i.e., more inertia.
Q47. A 1 kg stone thrown on ice slows due to:
Even on ice, there is some friction. This frictional force opposes the motion of the stone, causing it to slow down.
Q48. The acceleration of a 7-tonne train pulled by 40,000 N depends on:
According to Newton’s Second Law, acceleration depends on the net force and the mass of the object (a = F/m).
Q49. A hose ejecting water pushes fireman backward due to:
When water is ejected forward from the hose (action), the water exerts an equal and opposite force on the hose and fireman (reaction), pushing them backward.
Q50. Momentum is measured in:
The SI unit of momentum is kilogram-metre per second (kg·m/s), which can also be written as kg m s⁻¹.