The specific latent heat of fusion of ice is 336 kJ/kg. The heat required to melt 2 kg of ice at 0°C is:
A. 672 kJ
B. 1344 kJ
C. 336 kJ
D. 168 kJ
Answer: Option A
Solution (By JKSSB Mock Tests)
Heat for phase change Q = m·L_f, where L_f is latent heat of fusion. Thus Q = 2 kg × 336 kJ/kg = 672 kJ. This direct application tests calorimetry fundamentals. Memory aid: 'Latent heat: Q = mL; no temperature change during phase transition'. Competitive exams frequently test such calculations with standard values. Always ensure units match (kg and kJ/kg here); convert if necessary. This problem assesses basic formula application skills essential for thermodynamics sections.
Explanation:
Using the second equation of motion for free fall: h = ut + ½gt². Since it is dropped, initial velocity (u) = 0. Time (t) = 4s, g = 10 m/s². The height h = 0 + ½(10)(4)² = 5 × 16 = 80 meters.
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