Q&A - PSLE Science

[Newkiasu2011]

ms_lim:

Please help on this question :


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

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

B is elastic potential energy

[BOOMZ]

I don’t see anything wrong with your dd’s answer….

[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:

[BOOMZ]

Newkiasu2011:

Does CFC cause global warming?


CFC causes ozone layer depletion. Ozone is a green house gas and causes global warming. If CFC reduces ozone, then does it mean that CFC does not affect global warming.

I read that CFC itself is a greenhouse gas. In that case, it should cause global warming.

No CFC does not cause global warming. CFC and global warming are not related. The depletion of the ozone layer causes UV rays to penetrate into Earth but does not increase the temperature. For example, Australia is near the equator, where there is a large hole in the ozone layer, but that does not necessarily mean that the temperature is affected.

I am a student taking the same exam tomorrow so do please forgive me if I am wrong in one way or another.

[BOOMZ]

ss501:

hi,

The answer given is 4, pls help to explain, thanks.
http://i51.tinypic.com/2ufaib7.jpg\">

Evaporation occurs all the time. This is not to be mixed up with boiling. Although evaporation and boiling are both gain-heat processes, evaporation takes place all the time, in all temperatures. However, boiling takes place at only 100C for pure water. Thus, the answer is (4).

Please note that I am a student taking the PSLE so please forgive me if I have made any mistakes.

[Nebbermind]

BOOMZ:

No CFC does not cause global warming. CFC and global warming are not related. The depletion of the ozone layer causes UV rays to penetrate into Earth but does not increase the temperature. For example, Australia is near the equator, where there is a large hole in the ozone layer, but that does not necessarily mean that the temperature is affected.

I am a student taking the same exam tomorrow so do please forgive me if I am wrong in one way or another.

I agree with you that in general ozone depletion is associated with UV penetrating into Earth. I took the 'energy reaching the Earth' part from some website and now I'm not sure if that would be the correct reasoning.

While I know UV will cause damage to human cells, I'm not sure what other effect it has on other lifeform, eg, plants.

Perhaps someone can share.

[Nebbermind]

My advice to all taking the PSLE.


Go back to your schools mock exam ppr which has the prescribed answers and also the MOE recommended revision/summary book.

Some of the answer key for the past yr ppr may not be correct, so they will only add to the confusion.

[starlight1968sg]

BOOMZ:

Newkiasu2011:

Does CFC cause global warming?


CFC causes ozone layer depletion. Ozone is a green house gas and causes global warming. If CFC reduces ozone, then does it mean that CFC does not affect global warming.

I read that CFC itself is a greenhouse gas. In that case, it should cause global warming.

No CFC does not cause global warming. CFC and global warming are not related. The depletion of the ozone layer causes UV rays to penetrate into Earth but does not increase the temperature. For example, Australia is near the equator, where there is a large hole in the ozone layer, but that does not necessarily mean that the temperature is affected.

I am a student taking the same exam tomorrow so do please forgive me if I am wrong in one way or another.

Doubt this topic will be tested !
Anyway, is CFC a greenhouse gas? I thought it is a compound which reacts with ozone in the stratosphere, thus leading to the formation of an ozone hole. With this thinning of ozone layer, more UV light from the Sun can penetrates the atmosphere which thus warms up the Earth.

[BOOMZ]

Publica:

vidhyalog:

help with this one pls. http://i53.tinypic.com/5lqv4p.jpg\">

Hi vidhyalog,
Son thinks answer is (2). When the slingshot is released at point A, elastic potential energy is already converted to kinetic energy. Thus, sound, heat and gravitational potential energy will be present.

I think that the answer key is correct. When the slingshot is released, gravitational potential energy stored will then be converted to kinetic energy, not when the angry bird starts flying. Then, when the angry birds comes into contact with the objects at B, there will be frictional force between the objects and the angry bird thus heat and sound energy will be produced.

Please forgive me for any misinformation as I am also a student.

[BOOMZ]

starlight1968sg:

BOOMZ:

[quote=\"Newkiasu2011\"]Does CFC cause global warming?


CFC causes ozone layer depletion. Ozone is a green house gas and causes global warming. If CFC reduces ozone, then does it mean that CFC does not affect global warming.

I read that CFC itself is a greenhouse gas. In that case, it should cause global warming.

No CFC does not cause global warming. CFC and global warming are not related. The depletion of the ozone layer causes UV rays to penetrate into Earth but does not increase the temperature. For example, Australia is near the equator, where there is a large hole in the ozone layer, but that does not necessarily mean that the temperature is affected.

I am a student taking the same exam tomorrow so do please forgive me if I am wrong in one way or another.

Doubt this topic will be tested !
Anyway, is CFC a greenhouse gas? I thought it is a compound which reacts with ozone in the stratosphere, thus leading to the formation of an ozone hole. With this thinning of ozone layer, more UV light from the Sun can penetrates the atmosphere which thus warms up the Earth.[/quote]I'm not so sure but my Science teacher tells us that we should never be confused between global warming and Chlorofluorocarbons as they are not related.