Q&A - PSLE Science

[Cockroach]

When the water level reaches 40 ml, the air in the container will resist the rest of the water and prevent more from flowing in

[Tang]

vlim:

ms_lim:

Please help on this question :


http://i53.tinypic.com/o54xh2.jpg\">

Ans key : (1), dd's ans : (3)

My ds also choose (3)... :roll:

Hi,

Winding up a toy car:

Chemical potential energy --> Kinetic energy --> Elastic potentital energy.

So (1) is correct.

[Tang]

bcs-dad:

Hi All,


For the question below (for question part a), the answer key is \"Oxygen\". Can some body please explain this?

My DS answer is Carbon dioxide.

http://i51.tinypic.com/x1wwat.png\">

Thanks in advance..

Hi,

The answer is given in part b - oxygen.
The aim also mentions photosynthesis, so output is oxygen.

[Tang]

bcs-dad:

Hi All,


For the question below (for question part a), the answer key is \"Oxygen\". Can some body please explain this?

My DS answer is Carbon dioxide.

http://i51.tinypic.com/x1wwat.png\">

Thanks in advance..

Hi,

The answer is given in part b - oxygen.
The aim also mentions photosynthesis, so output is oxygen.

[Tang]

bcs-dad:

Hi All,


For the question below (for question part a), the answer key is \"Oxygen\". Can some body please explain this?

My DS answer is Carbon dioxide.

http://i51.tinypic.com/x1wwat.png\">

Thanks in advance..

Hi,

The answer is given in part b - oxygen.
The aim also mentions photosynthesis, so output is oxygen.

[atutor2001]

P6ians:

Dear atutor2001,

Air can be compressed,right?So why can't the volume of water be 60 ml?
TIA.

The pressure (force) exerted by the water in the funnel is very small. Therefore, it is unlikely for the air to be compressed by 20ml (i.e. another 20ml of water to flow in)

[atutor2001]

ms_lim:

Please help on part (b) :

http://i52.tinypic.com/9kvwug.jpg\">

The advantage is that we can select to switch on each bulb individually.

[ms_lim]

atutor2001:

ms_lim:

Please help on part (b) :

http://i52.tinypic.com/9kvwug.jpg\">

The advantage is that we can select to switch on each bulb individually.

Dear atutor2001, thank you for your help.

[atutor2001]

Verysuperkiasu:

Question:

Cutting down of trees will cause the phenomenon 'global warming'. Which of the following are involved in global warming?
A: burning of trees causes the carbon in the tree to combine with oxygen in the air to form carbon dioxide.
B: Carbon dioxide in the atmosphere acts as a blanket to trap heat in the Earth.
Without trees, Sun heats up te Earth's surface directly.
Soil erosion will destroy aquatic life forms, which in turn will enhance global warming subsequently.

(1) A and B only
(2) A, B and C only
(3) A, B and D only
(4) A, B, C and D

Answer is (4). My son doesn't think C and D are involved in global warming. Is he correct or is he wrong. His answer is (1).

The difficulty is in the interpretation of \"involved in global warming\". Many activities (C & D included) will involve global warming although they are not the main contributing factors. So I guess (4) is the answer because the question did not asked for the \"main cause\" of global warming.

[atutor2001]

Nebbermind:

atutor2001:

But option (4) specifically stated \"....but not in flask A\".

For science, this is a very strong statement and it would mean that not a tiny bit of milkiness is allowed in A.\"

I go for (1)

CO2 is a trace gas. While there may be precipitation (is that the right word?), I believe it's not enough to turn the water milky. I'll got for (4)

The duration of that experiment was not mentioned (missing). If the experiment is conducted for a few hours, I think A will definitely turn chalky. The reason is as follows :

Percentage of CO2 in exhaled air is about 4% and we can easily turn lime water chalky by blowing into it for 1 minute.

Percentage of CO2 in air is about 0.03. So if we increase the length of time by 270 times i.e. 270 minutes (4.5 hours), the lime water should also turn chalky. (270 times of 0.03 = 8.16 - although this is not a correct mathematical model it can provide a crude indication)