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Q.In the examples given below, which of the Newton's Law of Motion will apply ? Justify your answer. (1 + 1 = 2)

(a) When a Swimmer pushes the water backwards.
(b) When a cricket and tennis ball are thrown with the same force, the tennis ball moves with greater acceleration.
CBSECBSE Class XII Board 2026Subjective· 2mImportance★★★★★
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(a) Newton's Third Law — the swimmer's backward push on the water brings an equal and opposite forward reaction that propels him. (b) Newton's Second Law — with the same force, acceleration equals force divided by mass (a = F/m), so the lighter tennis ball accelerates more than the heavier cricket ball.

Concept understanding — the three laws in sports movement

Newton's laws explain every propulsion and projection in sport: the first law (inertia) describes the tendency of a body to resist a change in its state of motion; the second law gives the quantitative link between force, mass and acceleration (force = mass × acceleration); the third law states that every action has an equal and opposite reaction, the two forces acting on different bodies.

(a) Swimmer pushing the water backwards — Third Law

  1. The swimmer's stroke applies a force on the water in the backward direction — the action.
  2. By the third law, the water applies an equal and opposite force on the swimmer in the forward direction — the reaction.
  3. This reaction force is what propels the swimmer through the water. The action acts on the water and the reaction acts on the swimmer — they act on different bodies, which is why they do not cancel.

(b) Cricket ball vs tennis ball with the same force — Second Law

Force = mass × acceleration, so acceleration = force ÷ mass (a = F/m) — for a given force, acceleration is inversely proportional to mass. …

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