Q&A - PSLE Science

[atutor2001]

P5G:

Please help.


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TIA.

To me both (1) and (3) are possible options but I will pick (1) because of the words \"after a day\".

For some seeds, it will take a long time to germinate unless we soak the seek in water first (e.g. rice grain). So I am assuming that the time needed for a seed to germinate is primarily determined by the time needed for the seed to absorb sufficient water. Therefore, in the above experiment, during the period where there is no air, it allows time for the seed to get thoroughly soaked. Once air is introduced, the seed can carry out cell respiration immediately to release energy for germination to begin.

[atutor2001]

ms_lim:

Please help to explain Qn #25 from Pei Chun 2011 Prelim, Ans key is 2 :


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If I follow the language used in the options very strictly, my answer will also be (2) because option (4) says that the candle is not strong enough - does not make sense. I am presuming that what they mean is that the \"flame of the candle\" is not strong enough.

The reason why (2) was not pick is because paper is a poor conductor of heat so it takes time to transfer heat to the water. Similarly, water is also a poor conductor of heat and will not remove heat from the paper very quickly. There is also no mention of the temperature of the water so I presume that it must be at room temperature. Therefore, heat transfer from the point on the paper (where the flame is applied) to the water will be very slow and the paper should get burnt. A more likely reason why it takes a while for it to get burnt should be that the flame of the candle is not strong enough.

(This question is quite similar to the one whereby a piece of paper is wrapped around a rod with one half made of wood and the other half made of iron. The paper wrapped around the wooden half will get burnt when a flame is brought to the centre of the rod before the iron part)

[Verysuperkiasu]

Dear Atutor,


Some time ago, you mentioned volume of water decreases when temp decreases until about 4 deg, vol of water actually expands (even b4 solidifying).

How about melting process - where a bottle of ice is taken out of a freezer to melt. The question asked to observe
(a) the level of melted water
(b) the outer surface of the bottle. - (I think we can handle this part)

for (a) - melting process, ie, gaining heat - temp rises, does the volume of water increase or decrease? and why?

Thanking you in advance.

[atutor2001]

P5G:

Please help.


http://i55.tinypic.com/w1464n.gif\">


TIA.

My answer is (3) although I disagree with the words \"dissolved air in the milk powder\". It should be \"air trapped in the milk powder\"

[atutor2001]

P5G:

Please help.


http://i56.tinypic.com/16jj4mg.gif\">


TIA.

I will pick (2) because its twisted look appears to be more suitable for clinging to tree trunks.

[Nebbermind]

Verysuperkiasu:

Dear Atutor,


Some time ago, you mentioned volume of water decreases when temp decreases until about 4 deg, vol of water actually expands (even b4 solidifying).

How about melting process - where a bottle of ice is taken out of a freezer to melt. The question asked to observe
(a) the level of melted water
(b) the outer surface of the bottle. - (I think we can handle this part)

for (a) - melting process, ie, gaining heat - temp rises, does the volume of water increase or decrease? and why?

Thanking you in advance.

ice will take up a bigger volume that's why they float on water.

[atutor2001]

P5G:

Please help.


http://i51.tinypic.com/igb420.gif\">

TIA.

My answer is (1) because lifting J and M upwards is equivalent to lifting the corner that is opposite to X upwards and that will roll the ball to X.

[atutor2001]

P5G:

Please help.


http://i54.tinypic.com/1ypw1v.gif\">


TIA.

C and D are obvious choice but A is the questionable one. Some aquatic plant (floating/partially submerged type) has waxy leaf to prevent water from accumulating on the surface which could \"drown\" the leaves. However, most of them have hairy leaves to prevent water accumulation.

[Verysuperkiasu]

Nebbermind:

ice will take up a bigger volume that's why they float on water.

But the questions says 'Janice left the bottle of ice on the table to melt'. So it's not completely ice i think.

[ms_lim]

atutor2001:

ms_lim:

Please help to explain Qn #25 from Pei Chun 2011 Prelim, Ans key is 2 :


http://i55.tinypic.com/ehu0x.jpg\">

If I follow the language used in the options very strictly, my answer will also be (2) because option (4) says that the candle is not strong enough - does not make sense. I am presuming that what they mean is that the \"flame of the candle\" is not strong enough.

The reason why (2) was not pick is because paper is a poor conductor of heat so it takes time to transfer heat to the water. Similarly, water is also a poor conductor of heat and will not remove heat from the paper very quickly. There is also no mention of the temperature of the water so I presume that it must be at room temperature. Therefore, heat transfer from the point on the paper (where the flame is applied) to the water will be very slow and the paper should get burnt. A more likely reason why it takes a while for it to get burnt should be that the flame of the candle is not strong enough.

(This question is quite similar to the one whereby a piece of paper is wrapped around a rod with one half made of wood and the other half made of iron. The paper wrapped around the wooden half will get burnt when a flame is brought to the centre of the rod before the iron part)

Dear atutor2001,

Thank your for explaining. Is the ans (2)? Personally I think this is a bad question. Please correct me if I am wrong.