KVContributed by Kuldeep Verma — shared free on Ocoviz Open Learning
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Worked numericals applying Newton's three laws to everyday force and motion problems.
NEWTON'S LAWS — SOLVED EXAMPLES
Example 1 (First Law): A 2 kg book rests on a table. Explain why it doesn't move.
Answer: The table exerts a normal force equal and opposite to gravity (mg = 2 × 9.8 = 19.6 N upward), so net force = 0 → book stays at rest (inertia).
Example 2 (Second Law): A 5 kg cart is pushed with a force of 20 N. Find its acceleration.
Formula: F = ma → a = F/m
a = 20 / 5 = 4 m/s²
Example 3 (Third Law): A swimmer pushes water backward with 300 N. What pushes them forward?
Answer: By Newton's third law, the water pushes the swimmer forward with an equal and opposite reaction force of 300 N.
PRACTICE QUESTIONS
1. A 10 kg object accelerates at 3 m/s². Find the force applied.
2. Why does a rocket move forward when gas is expelled backward?
3. A 4 N force acts on a 2 kg mass. Find acceleration.