Lesson 38 39 questions – Specific Heat Capacity
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ALL
1What unit is used for all types of energy?
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2State the equation for the energy needed to raise the temperature of a particular material of known mass.
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3Use the following data to calculate the amounts of energy needed to change the temperature of the questions below.
Material / Specific heat capacity (J/kg ˚C)Copper / 380
Water / 4200
Aluminium / 880
Air / 1000
a)2kg of water by 5˚C
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b)500g of water by 4˚C
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c)100g of aluminium from 20˚C to 30˚C
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………………………………………………………………………………………… (2)
d)200 g of copper from 60˚C to 10˚C
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4A 2kg block of iron is given 10kJ of energy and its temperature rises by 10˚C. What is the specific heat capacity of iron?
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5Some cooks make toffee. Essentially, this is a process of boiling down a sugar solution to concentrate it and then allowing the liquid to cool until it sets. Small children are usually warned not to touch the cooling toffee for a very long time – much longer than the cooling for the same volume of pure water in the same vessel. Why do you think that the cooling period so long?
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6Show that the energy required to heat the air in your physics laboratory from a chilly 10 °C to a more comfortable 20 °C is about 3 000 000 J if it has the following dimensions: 3 m 10 m 10 m.
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7This question is about the operation of an electrically operated shower.
a)The water moves at constant speed through a pipe of cross section 7.5 x 10-5m2 to a showerhead. See the diagram. The maximum mass of water which flows per second is 0.090kgs-1.
i)Show that the maximum speed of the water in the pipe is 1.2ms-1.
Density of water = 1000kg m-3
(2)
ii)The total cross-sectional area of the holes in the head is half that of the pipe. Calculate the maximum speed of the water as it leaves the shower head.
Speed = ……………… ms-1 (1)
iii)Calculate the magnitude of the force on the showerhead.
Force = …………….. N (3)
b)The water enters the heater at the temperature of 15˚C. At the maximum flow rate of 0.090kgs-3, the water leaves the shower head at a temperature of 27˚C.
i)Calculate the rate at which energy is transferred to the water. Give a suitable unit for your answer.
Specific heat capacity of water = 4200Jkg-1K-1
Rate of energy transfer = ……………… unit …………….. (4)
ii)Suggest a reason that the power of the heater must be greater than your answer to (b)(i)
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………………………………………………………………………………………… (1)
iii)Calculate the maximum possible temperature of the water at the showerhead when the flow rate is half of the maximum.
Temperature = ………………….˚C (1)