Class 9 Science Force and Laws of Motion Extra Question Answer
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Q What is force?
Answer: Force is an external effort that can change the state of motion or shape of an object.
Q Name the three laws of motion stated by Newton.
Answer:
1. First Law (Law of Inertia)
2. Second Law (Force = Mass × Acceleration)
3. Third Law (Action and Reaction)
Q Define inertia.
Answer: Inertia is the property of a body to resist changes to its state of rest or uniform motion.
Q What does Newton’s First Law state?
Answer: An object remains at rest or in uniform motion unless acted upon by an external force.
Q Define momentum.
Answer: Momentum (p) is the product of the mass (m) of an object and its velocity (v): \( p = mv \).
Q State the formula for force based on the Second Law of Motion.
Answer: \( F = ma \), where \( F \) is force, \( m \) is mass, and \( a \) is acceleration.
Q What is the SI unit of force?
Answer: The SI unit of force is the Newton (N).
Q Explain Newton’s Third Law of Motion.
Answer: For every action, there is an equal and opposite reaction.
Q Why does a stationary car move backward when we push it forward?
Answer: The backward motion is due to the reaction force, as per Newton’s Third Law.
Q Give an example of balanced forces.
Answer: A book lying on a table experiences balanced forces—the table applies an upward force equal to the downward gravitational force.
Q What is unbalanced force?
Answer: An unbalanced force results in the change of motion or shape of an object.
Q Define frictional force.
Answer: Frictional force opposes the relative motion of two surfaces in contact.
