2) A new 75 m long concrete footpath is constructed down a Sydney street. Estima

Question

2) A new 75 m long concrete footpath is constructed down a Sydney street. Estimate how many 2 cm thick expansion joints are required to accommodate the change in length of the path from the coldest midwinter’s night to the hottest summer’s day

(Reference any data you need to look up!)

3)
a) If 70.8% of Earth’s surface is covered in water then how much energy is required to

heat the top 50 m of this water by 3 oC?

b) Assuming the Sun delivers an average of 1.2 kW m-2 to the side of Earth facing the Sun (think about what this means geometrically) and assuming no heat loss, how long will it take to for the heating in part a) to occur?

Explanation / Answer

3)

(a) Radius of the earth = 6.37*10^6 m

So, surface area = 4*pi*r^2 = 5.1*10^14 m^2

Volume of water= 0.708*A*50 = 1.8*10^16 m^3 = 1.8*10^19 kg

Amount of energy required = 1.8*10^19 * 4186 * 3

= 2.27*10^23 J

(b) Amount of energy reaching earth per second = 1200 J/m^2 * 5.1*10^14 *0.5

= 3.06*10^17

Time taken = 2.27*10^23 / 3.06*10^17

= 741830 sec

= 8.586 days

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