Q&A - PSLE Science

[vlim]

tianzhu:

vlim:

thanks tianzhu for your explaination..
But his reasoning is..the heat energy being absorbed by the black inner wall is transmitted away(sorry i don't how to use the exact word) through the aln box to the air outside...whereas the box with white interior, reflected the light and hence the light energy-> heat energy remain in the box...so the temperature in the box with white col is higher then tt of black col inner wall... :?

Hi vlim

I am sorry, I made a mistake.

My answer refers to heat absorbed by the black surface, I read the question again, and it’s about the temperature of the air inside the box, not the surface.

Best wishes

Thanks tianzhu!!
I always have a hard time when going through given model ans for past yr science exam papers with my son...He often disagree with the answer and argue with me abt the answer given...So nowadays,..i give up liao..if he think he is right then ok lo...but if his argument is wrong then jialet liao, he will give tt wrong answer again if tt qn appear in the exam
:thankyou:

[atutor2001]

vlim:

....so the model answer of that past yr exam paper is wrong..

If there is only 1 correct answer and your son's answer is correct, then by logical deduction, I think the model answer should be incorrect.

[tianzhu]

smartmummy:

I confused,for the sponge they said the air escaped when we squeezed,but here they said air compressed when we squeezed.

Hi

I’ve come across another question, it’s about a sponge being squeezed to take up a smaller space in a box.
If I remember correctly, the answer is “The sponge has a lot of air spaces in it and air can be compressed\"

I agree with you that air is being forced out rather than compressed.

Maybe, this is acceptable in P4 science for such question.

Best wishes

[smartmummy]

http://i55.tinypic.com/653k39.jpg\">

Hi Tianzu!
here is the sponge qn with answer.

[smartmummy]

http://i55.tinypic.com/20hrsao.jpg\">

Answer gave like as follows in the Assessment book Science Process Skills P3/4,

Yes,the stress ball is in the solid state.There are tiny air spaces inside the foam rubber which can be compressed when the ball is squeezed.As soon as the hand squeezing it is removed,the stress ball is able to return to its original shape and size.

[smartmummy]

Hi Tianzu!

I have posted two qns with answers provided in the respective books.
thank you.

[atutor2001]

Hi Smartmummy


Let us sort out what is the meaning of \"compressed\" first.

Case 1 : When we say that \"air is compressed\", we actually mean to say that \"the air is now occupying a smaller space\" (because the volume of air has decreased).

Case 2 : When we say that \"the spring is compressed\", we actually mean to say that \"the spring is now occupying a smaller space\" (but the volume of the spring itself is the same).

Therefore, there are 2 definitions for \"compressed\" :
(1) the space that something occupies is decreased because the volume of that thing is decreased or
(2) the space that something occupies is decreased but the volume of that thing remains the same\".

When we are dealing with the \"states of matter\", the word \"compressed\" refers strictly to definition (1) \"the volume of something is decreased\"

Hence, if we say that the \"air space\" is compressed, we would mean that the \"volume of the space (which is occupied by air)\" has been decreased. The confusion arises because \"space\" is not a matter and is also not covered in the science syllabus. The volume of an enclosed \"space\" can be decreased (compressed) by changing the shape of the space. (e.g. plastic bag)

Going back to squeezing a sponge - the volume of the space that was occupied by air did actually decreased. As such, it is ok to say that \"the air space is compressed, causing the air to escape.\" However, it would be wrong to say that \"the air in the sponge has been compressed.\"

Cheers

[Verysuperkiasu]

Pls help…


Question:
(Picture shows a styrofoam box with holes on top).
When X buys some fries, chef pokes holes on top of the styrofoam box as shown in the picture. Why?

Is the following explanation correct?
This is done so that any water vapour evaporating from the fries will exit through the holes and not condense on the inner surfaces of the styrofoam box to form water droplets which will drip on the fries and make them soggy.

[Verysuperkiasu]

Question 2


pictures show 3 ramps, one plain, 2nd one with 3 strips of paint, the 3rd one with 5 strips of paint.
A) state relationship between the time taken rolling down and the no of paint strips.
ans : the more the no of strips, the longer the time taken to roll down.

b) Explain your answer in a)
Is the following acceptable? (I am very cautious about keywords being missing in the answer - are all the keywords in the answer?)

Friction opposes motion. As there are more strips on the ramp, the amount of friction increases, hence the ball takes a longer time to roll down.

[tianzhu]

smartmummy:

Hi Tianzu!

I have posted two qns with answers provided in the respective books.
thank you.

Hi

Thank you for sharing the questions.

Best wishes