Q&A - PSLE Science

[cimman]

atutor2001:

I really feel bad for the kids. What used to be a 5-mark question for math in the 1990s (my kids' time) is now worth only 3 marks. I really can't see how kids can survive math with just model skill. Skill in simple algebraic manipulation and solving simultaneous equation are essential but most schools are not teaching.

Imo past year questions are better than assessment books. They are more up to date with the latest craze and also less errors.

All the best to your son.

Cheers

there is this assessment book, Challenging Mathematics Test Papers for Top Primary Schools. Publisher: math456.com. The questions there lend themselves to algebraic and simultaneous equation solutions. Very useful for students to sharpen their algebra skills.

[Verysuperkiasu]

cimman:

there is this assessment book, Challenging Mathematics Test Papers for Top Primary Schools. Publisher: math456.com. The questions there lend themselves to algebraic and simultaneous equation solutions. Very useful for students to sharpen their algebra skills.

Thanks for sharing!

[ck123]

Hi


What energy was possessed by a elastic band when it was stretched?

Ans : it has elastic potential energy

My question is answer just elastic energy correct?

Thanks

[ck123]

Does anyone has nanhua sa1 science 2011 paper can help to upload section B question 36.


Thanks

[hildangirl]

36a) Weight of object in the Scale pan


b) Type of Spring

c)

http://i54.tinypic.com/205udg.jpg\">

[ck123]

Hi Hildangirl


I need the question not answer thanks

[atutor2001]

cimman:

there is this assessment book, Challenging Mathematics Test Papers for Top Primary Schools. Publisher: math456.com. The questions there lend themselves to algebraic and simultaneous equation solutions. Very useful for students to sharpen their algebra skills.

Thank you very much. Next time when my friends ask, I can tell them to look for it.

[ivanhoo99]

atutor2001:

Verysuperkiasu:

1) Tom has a metal sieve with holes. He put some scraps of paper on it and place a flame below the sieve. Then he drill the holes bigger on the same sieve and repeat the experiment. Which set of scraps of paper will be more brown?

2) Mr Leong uses two metal sieves L and M (same no. of holes). He wants to find out which of the two sieves is a better conductor of heat. He place same scraps of paper on top of the 2 sieves. He observes that the paper inside sieve M looked more burnt than those inside L.

(i) Which sieve is made of a material that is a better conductor of heat.

(ii) Explain your answer in (i).

I heard the sieve conduct the heat away
It appears that M is a better conductor of heat because paper inside it turns browner means more heat get conducted through M. but answer is L. Why? same surface area in contact because same no of holes.

These 2 questions are very similar question to the burning of paper cup question. Understanding heat transfer alone is not enough. We also need to know :
1. Burning and flash point.
2. Temperature distribution.

My reasoning is as follows (sorry very lengthy) :

1. A material will burn only when its TEMPERATURE reaches a level we call \"flash point\". As long as the temperature on the sieve is less than the flash point of the paper, it will not turn brown. Flash point of paper is 232 degree C.

2. The temperature distribution of a metal sieve should roughly be highest at the centre where the flame is directly below and drops radially outwards. The temperature of a candle flame can be as high as 1400 degree C. However, the part of the metal sieve placed directly above the flame will be much lower because being a good conductor of heat, the metal sieve can transfer the heat away quickly from the source.

3. Therefore, a good conductor will have a lower temperature at the point where the flame source is. With lower temperature, the paper above it will not get burnt so easily.

4. A mesh with smaller holes will also have a lower temperature at the point where the flame source is because it has more metal surface and will be able to transfer heat away more quickly than one with big holes.

5. Therefore, if the same flame is used, the peak temperature of a good conductor will be lower compared to one that is a lousier conductor of heat. The temperature of a metal sieve with more metal surface will also have a lower temperature. They will cause less of the paper to get burnt.

Actually this is out of the syllabus but what to do.

[atutor2001]

ck123:

Hi


What energy was possessed by a elastic band when it was stretched?

Ans : it has elastic potential energy

My question is answer just elastic energy correct?

Thanks

Sorry, the word \"Potential\" is more important than the word \"elastic\" because it means \"stored energy.\"

[ivanhoo99]

ck123:

Hi


What energy was possessed by a elastic band when it was stretched?

Ans : it has elastic potential energy

My question is answer just elastic energy correct?

Thanks

Yes. It's wrong. Elastic energy have to come with the word potential. The and is correct.