Q&A - PSLE Science

[tianzhu]

Verysuperkiasu:

(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.

Hi

The moisture in the hot fries gets converted into water vapour.

The warm water vapour touches the cooler inner surface of the top cover of the styrofoam box and condenses as droplets of water.

The water then drips into the fries turning them soggy.

In reality, I am not too sure if all the water vapour escape through the openings in the cover .Small amount of them may still condense on the cover. Do an experiment when you buy fried chicken next time.

However, for PSLE science, I feel that your answer is acceptable.

Q45 from SCGS SA2 2009 is quite similar --- Please go to page 33 of this link.

http://www.orlesson.org/orp/09Sc/2009-P6-Science-SA2-SCGS.pdf

Hope this helps.

Best wishes

[tianzhu]

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.

Hi

For part (a) \"State\" signals write down the answer, not necessary to explain.
I think your answer is acceptable.

For part (b),I’d prefer to make some relationship with the context in the question.

Assuming a ball rolling down a ramp and the variables we are changing is the number of paint strips.

The larger number of paint strips increases the friction between the ball and the surface of the ramp causing the ball to take a longer time to roll down.

Hope this helps.

Best wishes

[Verysuperkiasu]

tianzhu:

Q45 from SCGS SA2 2009 is quite similar --- Please go to page 33 of this link.

http://www.orlesson.org/orp/09Sc/2009-P6-Science-SA2-SCGS.pdf

Hope this helps.

Best wishes

Thanks for your reply.

Saw the question 45 of SCGS paper - just wondering what the answer to 45b is - not included in the answer key - is the answer 'a tick for the second choice - that is open bag?

[Verysuperkiasu]

tianzhu:

Hi

For part (a) \"State\" signals write down the answer, not necessary to explain.
I think your answer is acceptable.

For part (b),I’d prefer to make some relationship with the context in the question.

Assuming a ball rolling down a ramp and the variables we are changing is the number of paint strips.

The larger number of paint strips increases the friction between the ball and the surface of the ramp causing the ball to take a longer time to roll down.

Hope this helps.

Best wishes

Uh..oh, my son's reply didn't specify friction between what and what .... think 1/2 a mark or 1 mark might be deducted. He has the bad habit of not being specific enough for section b.

thanks anyway, Tianzhu. Appreciate your help

:thankyou:

[tianzhu]

Verysuperkiasu:

Thanks for your reply.

Saw the question 45 of SCGS paper - just wondering what the answer to 45b is - not included in the answer key - is the answer 'a tick for the second choice - that is open bag?

Hi

You’re welcome.

Yes, you’re correct.

Putting the fries in the open paper bag allows the water vapour to escape, thus keeping the fries crispy for a longer period of time.

Best wishes

[stary]

Hi all, need explanation...


A bar magnet, QP, with poles denoted as shown, is suspended in the air. If another magnet, SR, shown in the diagram is brought near P, how would the bar magnet, QP move?

http://www.flickr.com/photos/64113082@N03/6089207068/in/photostream

1) A
2) B
3) C
4) D

Ans: 3

Fact is that the question did not state the poles of the magnet. They might be like poles and then repelled... Why?

Many thanks!

[Verysuperkiasu]

stary:

Hi all, need explanation...


A bar magnet, QP, with poles denoted as shown, is suspended in the air. If another magnet, SR, shown in the diagram is brought near P, how would the bar magnet, QP move?

http://www.flickr.com/photos/64113082@N03/6089207068/in/photostream

1) A
2) B
3) C
4) D

Ans: 3

Fact is that the question did not state the poles of the magnet. They might be like poles and then repelled... Why?

Many thanks!

Could there be some missing info on the diagram coz the question states 'with its poles denoted as shown'?

[Verysuperkiasu]

Picture shows an glass aquarium with aquatic plants and some animals like fish, waterboatman and water fleas. Tank is sealed with a glass plate and whole aquarium placed in a brightly lit room the whole day.


Qn : Which of the following statements is correct about the organisms after several months?

1) All the organisms will die as there is hardly any air in the tank
2) The plants can survive longer than the larger animals in the tank
3) The animals will all die in less than a day as there is insufficient air
4) The organisms could still survive as there is a continuous supply of air.
Answer is 2)

Son’s answer is 4) as there is a constant exchange of gases between the plants and animals - plants give out oxygen (during photosynthesis as the glass aquarium is placed in the light whole day) for the animals to take in and animals breathe out CO2 for the plants to take in. But my question is 'can this exchange of gases take place forever in a sealed container - is there a time limit to this? Note the question says ‘after several months’.

[Nebbermind]

stary:

Hi all, need explanation...


A bar magnet, QP, with poles denoted as shown, is suspended in the air. If another magnet, SR, shown in the diagram is brought near P, how would the bar magnet, QP move?

http://www.flickr.com/photos/64113082@N03/6089207068/in/photostream

1) A
2) B
3) C
4) D

Ans: 3

Fact is that the question did not state the poles of the magnet. They might be like poles and then repelled... Why?

Many thanks!

Since QP is suspended freely, it will rotate to align the unlike poles (like the compass needle), and then it will be attracted to the fixed magnet.

[Nebbermind]

Verysuperkiasu:

Picture shows an glass aquarium with aquatic plants and some animals like fish, waterboatman and water fleas. Tank is sealed with a glass plate and whole aquarium placed in a brightly lit room the whole day.


Qn : Which of the following statements is correct about the organisms after several months?

1) All the organisms will die as there is hardly any air in the tank
2) The plants can survive longer than the larger animals in the tank
3) The animals will all die in less than a day as there is insufficient air
4) The organisms could still survive as there is a continuous supply of air.
Answer is 2)

Son's answer is 4) as there is a constant exchange of gases between the plants and animals - plants give out oxygen (during photosynthesis as the glass aquarium is placed in the light whole day) for the animals to take in and animals breathe out CO2 for the plants to take in. But my question is 'can this exchange of gases take place forever in a sealed container - is there a time limit to this? Note the question says 'after several months'.

FOOD?!