WAEC 2017 Physics · Question 29

Ice of mass 50g at 0°C was completely melted by 70% of the total heat energy supplied. Calculate the total…

Question

Ice of mass 50g at 0°C was completely melted by 70% of the total heat energy supplied. Calculate the total heat energy supplied [Specific latent heat of fusion of ice = 336 $Jg^{-1}$ ]

A.2400J
B.6800J
C.7251J
D.24000J

Answer: D. 24000J

Explanation written with AI and checked against the answer key

Analyze the question: 50 g of ice at 0°C melts completely. Only 70% of the total heat supplied is used for melting. We need the total heat supplied. Concept: Heat needed to melt ice at its melting point is Q = m × L where m is the mass and L is the specific latent heat of fusion. Solution: Step 1: Heat actually used to melt the ice Q = mL = 50 g × 336 J/g = 16,800 J Step 2: This is only 70% of the total heat supplied (E) 0.70 × E = 16,800 E = 16,800 ÷ 0.70 = 24,000 J Tip: When a question says "only x% of the energy is useful", always set up: useful energy = efficiency × total energy. Then divide the useful energy by the percentage to get the total. The total must always be larger than the useful part, so you can rule out options like A and B (2400 J and 6800 J), which are smaller than 16,800 J.

AI can make mistakes. Report anything that looks wrong.