Force and Laws of Motion — Important Questions

Mass × Velocity

Step 1: Momentum (p) is defined as the product of mass and velocity: p = mv. Step 2: It measures the 'quantity of motion' an object possesses. Step 3: Momentum has both magnitude and direction (same as velocity direction). Step 4: Its SI unit is kg m/s. Step 5: Other options are incorrect: ma gives force, F×t gives impulse (change in momentum), and mass×distance has no physical significance in mechanics.

To increase the time of impact and reduce the force

Step 1: When catching a ball, the ball's momentum must change from mv to 0. Step 2: By Newton's second law, Force = change in momentum/time taken. Step 3: By moving hands backward, the fielder increases the time taken to stop the ball. Step 4: Since F = Δp/Δt, when time increases, force decreases for the same momentum change. Step 5: This reduces the impact force on hands, preventing injury. The momentum change remains same, but force is reduced.

A book resting on a table

Step 1: Balanced forces occur when multiple forces acting on an object cancel each other out. Step 2: For a book on a table, gravitational force pulls it down with force mg. Step 3: The table exerts an equal upward normal force on the book. Step 4: Since these forces are equal and opposite, they balance each other, keeping the book at rest. Step 5: Other options show unbalanced forces: falling book has net downward force, accelerating car has net forward force, kicked ball has applied force.

Continue moving in a straight line at constant speed unless acted upon by an unbalanced force

Step 1: Newton's first law states that objects in motion tend to stay in motion with constant velocity. Step 2: This motion continues in a straight line unless an external unbalanced force acts on it. Step 3: This property is called inertia - resistance to change in motion state. Step 4: In real life, friction acts as the unbalanced force that eventually stops moving objects. Step 5: Other options are wrong: objects don't stop on their own (needs force), don't accelerate without force, and don't change direction without external force.