F3 PHY (HEAT 2) EASY!

KIKI YEUNG

2010-05-22 5:42 am

.下有D關於S3 PHY ( HEAT )既問題
有D有答案但5明點解希望有人幫到我!
1 Which one would cool a cup of hot drink to a lower temperature, water bath of mass 1kg at 0 degrees Celesius or ice of mass 0.2kg at 0 degrees Celesius? Explain briefly with calculations.
(ANS: ICE)

2 Why is black sand added to the chestnuts when they're being roasted?

3 Is it always true that we'll feel cooler when we touch the object which is a good conductor(eg. metal) than an object which is a poor conductor(eg wood)?

BIO
1. Which of the following chemical substances can provide the body with energy?
A. carbohydrates, fats and proteins only
B. carbohydrates, fats, proteins and nucleric acids only

D ANS 5使長篇大論
答案要肯定
5肯定既話就飛左佢LA
ＴＨＸ　：）

回答 (1)

天同

2010-05-22 6:04 am

✔ 最佳答案

1. When ice at 0'C turns into water at 0'C, it absorbs latent heat. The latent heat of fusion of ice is 334000 J/kg, thus 0.2 kg of ice will absorb 66800 J of more energy to cool down the drink.

2. This would spread the heat out evenly onto the surface of chestnut, so as to avoid the chestnut being over roasted on one side but under done on the other side.
3. Under the same evironmental conditions, this is generally true.
The rest are not physics question, sorry...can't help.

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