According to Newton's third law, action and reaction forces:
A. Act on the same body and cancel each other
B. Act only when bodies are in contact
C. Are always equal to weight of the body
D. Act on different bodies and never cancel each other
Answer: Option D
Solution (By JKSSB Mock Tests)
Newton's third law states: for every action, there is an equal and opposite reaction. These forces act on two different interacting bodies, hence they never cancel each other as they don't act on the same body. They can act at a distance (e.g., gravitational forces) or through contact. Cancellation of forces occurs only when multiple forces act on a single body. This distinction is crucial for free-body diagram analysis. Exam tip: Always identify which body each force acts upon. Misconception about force cancellation is a common trap in competitive exam questions testing Newton's laws.
Explanation:
Linear expansion formula: ΔL = L₀αΔT, where ΔT = T - T₀. Thus new length L' = L₀ + ΔL = L₀[1 + α(T - T₀)]. Option A incorrectly uses absolute temperature T instead of temperature change. Option C gives only the change, not total length. Option D uses initial temperature incorrectly. Memory aid: 'Expansion depends on temperature change, not absolute value'. This standard formula application is common in thermal physics questions. Always identify initial length and temperature reference point to avoid sign errors.
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