Two objects of masses 1 kg and 4 kg have equal momentum. What is the ratio of their kinetic energies?
A. 1:2
B. 2:1
C. 4:1
D. 1:4
Answer: Option C
Solution (By JKSSB Mock Tests)
Kinetic Energy (K) is related to momentum (p) by the formula K = p² / 2m. Since they have equal momentum, p is constant. Therefore, K is inversely proportional to mass (K ∝ 1/m). Ratio of kinetic energies K1/K2 = m2/m1 = 4/1 = 4:1. The lighter object has more kinetic energy.
Explanation:
Light year: distance light travels in one year in vacuum ≈ 9.46×10¹⁵ m. Astronomical distance unit, not time. Memory aid: 'Light year = speed × time = distance'. Unit knowledge frequently tested in competitive exams to avoid common misconception about light year being time unit.
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