According to Newton's third law, action and reaction forces:
A. Act on the same body and cancel each other
B. Are always equal to weight of the body
C. Act only when bodies are in contact
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:
The volume of a sphere is given by V = (4/3)πr³. The formula for relative error in volume is (ΔV/V) = 3 × (Δr/r). Since the percentage error in radius (Δr/r × 100) is 2%, the percentage error in volume will be 3 × 2% = 6%. Constants like 4/3 and π do not contribute to the error.
Explanation:
Spectrometer measures wavelengths of light using diffraction gratings or prisms to disperse light and angular measurements. Interferometer (D) can also measure wavelength but spectrometer is the standard instrument for spectral analysis. Microscope and telescope magnify images, not measure wavelength. Memory tip: 'Spectrometer = wavelength measurement via dispersion; used in spectroscopy'. This instrument-application question tests practical physics knowledge, frequently examined in competitive exams. Always associate instruments with their primary function; competitive exams often test context-specific uses.
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