The scientist who formulated the universal law of gravitation is:
A. Isaac Newton
B. Galileo Galilei
C. Johannes Kepler
D. Albert Einstein
Answer: Option A
Solution (By JKSSB Mock Tests)
Isaac Newton formulated the universal law of gravitation in his Principia Mathematica (1687), stating F = Gm₁m₂/r². Galileo studied falling bodies; Kepler derived planetary motion laws; Einstein developed general relativity (gravity as spacetime curvature). Memory aid: 'Newton = gravity apple story'. This history-based question tests knowledge of key scientific contributions, frequently appearing in competitive exams. Always associate scientists with their specific discoveries to avoid confusion between classical and modern physics pioneers.
A block of mass 'm' is placed on a rough inclined plane of inclination theta. If the block is just on the verge of sliding down, the coefficient of static friction (mu) is equal to:
Explanation:
When the block is on the verge of sliding (limiting friction), the downward component of weight along the plane equals the maximum static friction force. mgsin(theta) = mu * N. The normal reaction N is balanced by the perpendicular component of weight: N = mgcos(theta). Dividing the two equations gives mgsin(theta) / mgcos(theta) = mu, so mu = tan(theta). This angle is called the angle of repose.
Explanation:
Electrical resistance (R) is Voltage/Current. Voltage (V) is Work/Charge. Work is [ML^2T^-2] and Charge is [AT]. So, V = [ML^2T^-3A^-1]. Therefore, R = V/A = [ML^2T^-3A^-2]. Memorizing the dimensional formula for resistance is highly recommended for competitive exams.
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