Newton’s First Law of Motion – Long Answer Questions
Medium Level (Application & Explanation)
Q1. State Newton’s First Law of Motion and explain it with two everyday examples.
Answer:
- Newton’s First Law is the Law of Inertia.
- It says an object stays at rest or in uniform motion unless an unbalanced external force acts on it.
- A book on a table stays at rest until you push it.
- A soccer ball keeps rolling until friction or a kick stops or changes it.
- The law explains both starting and stopping of motion.
- It links motion changes to forces acting on objects.
Q2. What is inertia? How does it depend on mass? Give examples.
Answer:
- Inertia is the tendency to resist change in state of motion.
- More mass means more inertia.
- A heavy rock is harder to start or stop than a small stone.
- A loaded cart needs more force than an empty cart to move or stop.
- Your body keeps moving forward when a car suddenly stops.
- This shows inertia of motion acting on your body.
Q3. Differentiate between balanced and unbalanced forces with effects on motion.
Answer:
- Balanced forces are equal and opposite.
- They make the net force = 0.
- There is no change in speed or direction in this case.
- Unbalanced forces are unequal.
- They cause acceleration, deceleration, or change in direction.
- A tug-of-war with equal pulls is balanced; a stronger team creates unbalanced force and motion.
Q4. Explain why seat belts are important using the Law of Inertia.
Answer:
- In a moving car, your body has inertia of motion.
- If the car stops suddenly, your body wants to keep moving forward.
- A seat belt provides the needed unbalanced external force to stop your motion safely.
- It spreads the stopping force over a short time and larger area.
- This reduces injury to the chest and head.
- Thus, seat belts use the first law to protect you.
Q5. Describe the role of friction as an external force in the First Law. Use examples.
Answer:
- Friction is an external force that opposes motion.
- It changes an object’s state of motion.
- A hockey puck slides longer on ice because friction is less.
- The same puck stops quickly on a rough floor due to more friction.
- Without friction, objects would keep moving in straight lines.
- So, friction often acts as the unbalanced force that stops motion.
High Complexity (Analysis & Scenario-Based)
Q6. A bus stops suddenly and passengers lurch forward. Analyze this using the First Law and suggest safety measures.
Answer:
- Passengers have inertia of motion with the moving bus.
- When the bus stops, the body tends to continue forward.
- There is no equal opposing force on the body at that instant.
- This causes the forward lurch.
- Seat belts, holding rails, and keeping feet apart help create safe opposing forces.
- Drivers should brake gradually to reduce sudden unbalanced forces.
Q7. Two carts, A (light) and B (heavy), are pushed with the same force on a smooth floor. Predict and explain their motion.
Answer:
- Cart B has more mass and thus more inertia.
- With the same unbalanced force, Cart A gets more acceleration.
- Cart B speeds up more slowly due to higher inertia.
- On a smooth floor, friction is small, so the effect of mass is clearer.
- If the push stops, both keep moving with uniform velocity.
- This is due to the First Law and low friction.
Q8. An astronaut in space pushes a tool away. What happens to the tool and the astronaut? Explain using the First Law.
Answer:
- In space, friction and air resistance are almost zero.
- The tool moves with uniform velocity in a straight line.
- The astronaut also moves in the opposite direction due to reaction.
- Without other external forces, both keep moving.
- To stop, they need an unbalanced force, like firing a thruster.
- This shows the persistence of motion in low-friction environments.
Q9. A book rests on a table. Identify all forces, judge if they are balanced, and predict motion if a small push is applied.
Answer:
- The book has weight downward and normal reaction upward.
- These forces are equal and opposite, so they are balanced.
- The net force is zero, so the book stays at rest.
- A small horizontal push adds an unbalanced force.
- If the push is enough to overcome friction, the book will start moving.
- Once the push stops, friction slows and stops it.
Q10. In a balloon rocket activity, the balloon zooms forward when air rushes out. Analyze the forces and link to the First Law.
Answer:
- Air rushes out backward, creating an unbalanced external force forward.
- The balloon’s state of motion changes from rest to acceleration.
- If air flow stops and friction is small, it would move with uniform speed.
- In real life, air resistance and string friction slow it down.
- The motion continues until opposing forces balance it or stop it.
- This shows both the need for an unbalanced force to start motion and the role of resistive forces to stop it.