JEE Main · 2011 · 10 Apr 2011 · Offline · Heat & Thermodynamics

100 g of water is heated from

3 0^{0} C

5 0^{0} C

. Ignoring the slight expansion of the water, the change in its internal energy is (specific heat of water is

4148 J / kg / K

) :

(A)8.4 kJ✓ Correct
(B)84 kJ
(C)2.1 kJ
(D)4.2 kJ

Answer: (A)

Solution

Because the water barely expands, no work is done, so by the first law the internal-energy change equals the heat supplied,

Δ U = Δ Q = m s Δ T

. With

m = 0.1 kg

s = 4148 J k g^{- 1} K^{- 1}

and

Δ T = 20 K

Δ U = 0.1 \times 4148 \times 20 \approx 8.3 \times 1 0^{3} J

, about

8.4 kJ

JEE Main · 2011 · 10 Apr 2011 · Offline · Single correct option

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