JEE Main · 2026 · 21 Jan 2026 · Shift 1 · Heat & Thermodynamics

A gas based geyser heats water flowing at the rate of 5.0 litres per minute from

2 7^{\circ} C

8 7^{\circ} C

.
The rate of consumption of the gas is ____ g/s.
(Take heat of combustion of gas

= 5.0 \times 1 0^{4} J / g

) specific heat capacity of water

= 4200 J / kg .^{\circ} C

(A)2.1
(B)4.2
(C)0.42✓ Correct
(D)0.21

Answer: (C)

Solution

The flowing water carries away heat at the rate

\overset{m}{˙} c Δ T

, with

\overset{m}{˙} = 5 L/min = \frac{5}{60} kg/s

c = 4200 J k g^{- 1}^{\circ} C^{- 1}

and

Δ T = 87 - 27 = 60^{\circ} C

. This power is

\frac{5}{60} \times 4200 \times 60 = 21000 W

. If the gas burns at

x

grams per second it supplies

x \times 5.0 \times 1 0^{4} W

; equating the two,

x = \frac{21000}{5.0 \times 1 0 ^{4}} = 0.42 g/s

JEE Main · 2026 · 21 Jan 2026 · Shift 1 · Single correct option

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