JEE Mains · Physics · STD 11- Mechanical properties of solids
- JEE Mains 2026
- Hard
- Numerical
The heat extracted out of \(x\) gram of water initially at \(50°C\) to cool it down to \(0°C\) is sufficient to evaporate \((1000 - x)\) gram of water also initially at \(50°C\). The value of \(x\) (closest integer) is _______.
(Take latent heat of water \(2256\text{ kJ/kg.K}\), specific heat capacity of water \(4200\text{ J/kg.K}\))
Pick an option to check your answer.
Answer & Solution
Correct Answer
(B) 922
Step-by-step Solution
Detailed explanation
Heat extracted to cool \(x\) gram of water from \(50^{\circ}\text{C}\) to \(0^{\circ}\text{C}\) is given by:
\(Q_1 = m_1 c \Delta T_1\)
\(Q_1 = x \times 4.2 \times (50 - 0) = 210x \text{ J}\)
Heat required to raise the temperature of \((1000 - x)\) gram of water from \(50^{\circ}\text{C}\) to \(100^{\circ}\text{C}\) and evaporate it is given by:
\(Q_2 = m_2 c \Delta T_2 + m_2 L\)
\(Q_2 = (1000 - x) \times [4.2 \times (100 - 50) + 2256]\)
\(Q_2 = (1000 - x) \times (210 + 2256) = 2466(1000 - x) \text{ J}\)
Equating the heat extracted and the heat required:
\(Q_1 = Q_2\)
\(210x = 2466(1000 - x)\)
\(210x = 2466000 - 2466x\)
\(2676x = 2466000\)
\(x = \dfrac{2466000}{2676} \approx 921.52\)
The closest integer value for \(x\) is \(922\).
Answer: \(922\)
\(Q_1 = m_1 c \Delta T_1\)
\(Q_1 = x \times 4.2 \times (50 - 0) = 210x \text{ J}\)
Heat required to raise the temperature of \((1000 - x)\) gram of water from \(50^{\circ}\text{C}\) to \(100^{\circ}\text{C}\) and evaporate it is given by:
\(Q_2 = m_2 c \Delta T_2 + m_2 L\)
\(Q_2 = (1000 - x) \times [4.2 \times (100 - 50) + 2256]\)
\(Q_2 = (1000 - x) \times (210 + 2256) = 2466(1000 - x) \text{ J}\)
Equating the heat extracted and the heat required:
\(Q_1 = Q_2\)
\(210x = 2466(1000 - x)\)
\(210x = 2466000 - 2466x\)
\(2676x = 2466000\)
\(x = \dfrac{2466000}{2676} \approx 921.52\)
The closest integer value for \(x\) is \(922\).
Answer: \(922\)
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