A rating of 5 kW means it gives heat at the rate of 5 kJ per second

If we consider 1 minute:

5 kW = 5000 J s-1 = 5000 x 60 J min-1 = 300000 J min-1

In 1 minute 5 Kg of water pass through the shower unit.

Q = M c DT.

30000 = 5 x 4180 x DT

DT = 14.4

The final temperature = 15

**Q 40**

Assume that the heat lost from the iron goes
into just melting the ice and does not raise its temperature

Q (lost) = Q
(gained)

mcDT (iron) = mL_{f }(ice)

0.1 x 460 x (150
- 0) = m x 3.34 x 10^{5
}
6900 = m x 3.34 x 10^{5
}
m = 0.0206 kg (= 20.6 g)

Density (D) =
m/V

Density of ice at 0^{o}C is 0.9162 g/cm^{3}

V = m/D = 20.6/0.9162 = 22.48 cm^{3
}Length of cylinder =
Volume/Area = 22.48/(p r^{2})

L =
22.48/(p x 2^{2}) = 1.79 cm (the answer in back of the book says 1.9 cm and this is wrong).

My thanks to Oscar Lee from St Joseph's College, Gregory Terrace, Brisbane for pointing out the error.

I'd normally send him a packet of Tim Tams but as they are made with palm oil I've stopped buying them. Sorry Oscar.

Assume that the steam cools to 100°C, condenses to water at 100°C and then cools to 0°C. At the same time the ice cube melts and turns to water at 0°C

Q (lost) = Q (gained)

mcDT + mL

m = 2.48 g

\ m (total) = 55 g + 2.48 g = 57.48 g

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