JEE Mains Model Paper 15

heat released by 5 kg of water when its temperature falls from 20°C to 0°C
Q1 = cm (ΔT) = 103 × 5 × 20 = 0.2 × 105 cals
This heat is used in raising the temp, of 2 kg of ice at -20° C to 0°C and then melting it subsequently.
Heat energy taken by 2kg of ice at - 20°C in coming to 0°C is
Q2 = cmΔT = 500 × 2 × 20 = 0.2 × 105 cal
The remaining heat
Q = Q1−q2 = 0.8 × 105 cal
Mass of ice melted m' =

Q

L

=

0.8×105

80×103

= 1 Kg
∴ Temperature of mixture will become 0°C
Mass of water in it = 5 + 1 = 6 kg
Mass of ice left in it = 2 - 1 = 1 kg.