Q&A - PSLE Science

[atutor2001]

Cockroach:

http://i52.tinypic.com/2yywjmt.jpg\">

someone help pls
TIA

This is a tricky question. When 40 ml of water has been poured into the container, the water in the container will cover the bottom end of the air tube. Air can no longer escape and is trapped in the container. So the answer is 40 ml

[ss501]

hi atutor2001,


Thank you very much for your help, really appreciate it

[ss501]

hi,

The answer given is 3, pls help to explain, thanks.
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[ss501]

hi,

The answer given is 2, pls help to explain, thanks.
http://i51.tinypic.com/jsezdi.jpg\">

[atutor2001]

ss501:

hi,

The answer given is 3, pls help to explain, thanks.
http://i51.tinypic.com/2wgyt1h.jpg\">

Compare the boxes first :
Amount of heat in box without bulb is relatively unchanged (depends only on conduction through the box)
Amount of heat in box is increasing continuously because of the bulb.

If heat is not added to the box, the surrounding temperature will remain relatively unchanged and the temperature of the water in cup P & Q will be about the same. So the rate of evaporation in both cups are about the same.

If heat is added continuously, temperature of surrounding air keeps increasing. Metal cup R absorbs heat faster than styrofoam cup S so temperature of water in metal cup R will be higher than temperature of water in styrofoam cup S. Therefore, water in metal cup R evaporates faster than styrofoam cup S.

[atutor2001]

ss501:

hi,

The answer given is 2, pls help to explain, thanks.
http://i51.tinypic.com/jsezdi.jpg\">

Gravity or gravitational force is the force that Earth pulls on the ping pong ball. The heavier (bigger mass) the ball is, the greater will be this force. Gravitational force is actually the weight of the ball.

If there is no gravity, the ping pong ball will keep flying upwards after being fired from the gun. It is gravity that pulls the ping pong down back to the ground. This caused the ball to move in a curved path.

Therefore, option (B) looks ok to me, except for the word \"more\". If there is an option (B) & (C), I will take it.

Air resistance is the frictional force between the ball and the surround air as the ball flies through the air. Greater air resistance will slow down the ball faster and the ball will move a shorter distance.

[P.047330KH]

http://i54.tinypic.com/33copz4.jpg\">

Hi, can anyone please help with this question? The ans given is (4), but I think it should be (1). :?:

[Crispycreepy]

[quote=\"P.KH\"]http://i54.tinypic.com/33copz4.jpg\">

Hi, can anyone please help with this question? The ans given is (4), but I think it should be (1). :?:
The surrounding air that enters beaker A also contains carbon dioxide that will change the limewater chalky , however the amount is minimal. In contrast most the 21% of oxygen that was in the surrounding air was converted to carbon dioxide by the mice , thus the change in beaker B was more significant.

[atutor2001]

Crispycreepy:

The surrounding air that enters beaker A also contains carbon dioxide that will change the limewater chalky , however the amount is minimal. In contrast most the 21% of oxygen that was in the surrounding air was converted to carbon dioxide by the mice , thus the change in beaker B was more significant.

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)

[P.047330KH]

atutor2001:

Crispycreepy:

The surrounding air that enters beaker A also contains carbon dioxide that will change the limewater chalky , however the amount is minimal. In contrast most the 21% of oxygen that was in the surrounding air was converted to carbon dioxide by the mice , thus the change in beaker B was more significant.

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)

Thanks a lot for your answer. Am happy my answer is correct ..

Seconldy, Is there anywhere I can get hold of Nanyang and Nanhua Prelims paper for 2011??