Force and Laws of Motion — Flashcards
Karnataka Board · Class 9 · Science
20 flashcards for Force and Laws of Motion (Karnataka Board Class 9 Science) to test yourself on key terms and facts.
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A cricket fielder pulls his hands backward while catching a fast-moving ball. Why does he do this?
Answer
The fielder increases the time during which the ball's velocity decreases to zero. According to Newton's second law (F = ma), when time increases, acceleration decreases, which reduces the force on hi…
What is inertia and how does it relate to mass?
Answer
Inertia is the natural tendency of an object to resist change in its state of motion or rest. Mass is the measure of inertia - heavier objects have more inertia. For example, it's easier to push an em…
A motorcar of mass 1000 kg moving at 30 m/s stops in 4 seconds when brakes are applied. Calculate the force exerted by the brakes.
Answer
Given: m = 1000 kg, u = 30 m/s, v = 0 m/s, t = 4 s Using F = m(v-u)/t F = 1000 × (0-30)/4 = 1000 × (-30)/4 = -7500 N The negative sign indicates the force opposes motion. The magnitude of braking forc…
Why do we fall backward when a bus suddenly starts moving?
Answer
When the bus starts suddenly, our feet move with the bus due to friction, but our upper body tends to remain at rest due to inertia (Newton's First Law). This creates a relative backward motion of our…
What happens when you flick a card with a coin on top of it placed over a glass?
Answer
The card moves away quickly, but the coin falls straight down into the glass due to inertia. The coin tends to remain at rest (Newton's First Law) even when the card is removed suddenly. This happens …
Define momentum and state its SI unit.
Answer
Momentum is the product of an object's mass and velocity: p = mv. It has both magnitude and direction (same as velocity). The SI unit of momentum is kg⋅m/s (kilogram meter per second). Momentum repres…
A gun recoils when fired. Explain this phenomenon using Newton's third law.
Answer
When a gun is fired, it exerts a forward force on the bullet (action). The bullet exerts an equal and opposite force on the gun (reaction). Since the gun has much greater mass than the bullet, its acc…
What are balanced and unbalanced forces? Give examples.
Answer
Balanced forces: Equal forces acting in opposite directions that cancel each other out, causing no change in motion. Example: A book on a table (weight balanced by normal force). Unbalanced forces: Ne…
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Sources & Official References
- Karnataka SSLC — kseeb.kar.nic.in
- Dept of Pre-University Education, Karnataka
- National Education Policy 2020 — education.gov.in
Content is aligned to the official syllabus. Refer to the board website for the latest curriculum.
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