Q&A - PSLE Science

[Tang]

Hi,


My sister’s answer is "circle" and I hope that she is correct.

[Tang]

chrisu:

You are right, they don't put that in Science. Does that mean drawn to scale? Haha, what can I say then? It makes me think of nowadays a lot of ads also quote \"picture shown only for reference. Actual item may differ from picture shown\"...so what is shown may or may not be what is shown, it's difficult to assume.


BTW Tianzhu, the Science teacher had informed the boy in my daughter's class about the 2 balls collision answer just before they sat for the PSLE Science exam yesterday. Now the teacher said the answer is (1) after confirmation with the Science HOD without explanation. Answer (1) is;
http://img.photobucket.com/albums/v160/guppiesonli/Misc/F1.jpg\">

I've read the link you've given last Sunday, thanks. I played snooker but to achieve elastic collision needs certain level of skill.

atutor2001:

[quote=\"chrisu\"]As it's Science question, unless the question specified that the diagram shown is actual size, I think it's unfair to expect the students to draw lines to see the shadow cast. If the diagram shown is actual size or in good ratio proportion, then drawing straight lines from the light source is a good way to see the shadow cast. Otherwise we can only guess the actual distance between objects and light source.

Maybe you have not noticed. In math geometry question, all questions will have the print \"Not draw to scale\". However, we seldom see such wordings in Science questions. Hope you understand what I mean.

[/quote]
Hi,

My answer is (1) as some energy has been converted to sound energy and heat energy.

[Verysuperkiasu]

Tang:

Hi,


My sister's answer is \"circle\" and I hope that she is correct.

circle should be correct.

[vlim]

Verysuperkiasu:

Cheerfuldad:

Hi VSkiasu,

My DS put square as well. According to my son, the distance between the circle and the square is 0. i.e. side by side. Therefore, my DS concluded is square.

Thanks for your sharing.....but they say just extend the straight lines from the pinhole to the objects - the circle is the one which is blocking the light - the lines didn't touch the bigger square. But i wish the answer was 'square'.

second thought if the distance betw the big square and the ball is very near to each other or 0 distance...then the answer might be square hor.. :? ....hope can see the picture ..

[Verysuperkiasu]

vlim:

Verysuperkiasu:

[quote=\"Cheerfuldad\"]
Hi VSkiasu,

My DS put square as well. According to my son, the distance between the circle and the square is 0. i.e. side by side. Therefore, my DS concluded is square.

Thanks for your sharing.....but they say just extend the straight lines from the pinhole to the objects - the circle is the one which is blocking the light - the lines didn't touch the bigger square. But i wish the answer was 'square'.

second thought if the distance betw the big square and the ball is very near to each other or 0 distance...then the answer might be square hor.. :? ....hope can see the picture .. [/quote]dont know leh. tmr ask ds to ask teacher.

[kittycat01]

I have a question.


The picture in the question shows a plant in a sealed beaker of soil (only the bottom part of the plant that means the root part is sealed in the beaker). But there’s some water in the sealed beaker. The whole plant is sealed in a clear container and put out in the sun. Quesion says the rate of photosynthesis is decreasing…and is due to what? is it carbon dioxide or water. To answer the question must ask ourselves which one is used up first - carbon dioxide or water?

[kittybank]

[Verysuperkiasu]

wormy:

If circle is not big enough, the corners of the square will show. Hence it will look like a square

but height of circle (diameter) is same as the length of square. so everyone thinks it's a square. think is a trick question. u have to look at the distance between the light source and the objects. It is a square only when the light source is very far away. The only way to find out in the question is to draw straight lines from light source to the objects. Whichever one blocks the light will be that shadow on the screen. seems like circle Think so...

[atutor2001]

kittycat01:

I have a question.


The picture in the question shows a plant in a sealed beaker of soil (only the bottom part of the plant that means the root part is sealed in the beaker). But there's some water in the sealed beaker. The whole plant is sealed in a clear container and put out in the sun. Quesion says the rate of photosynthesis is decreasing.....and is due to what? is it carbon dioxide or water. To answer the question must ask ourselves which one is used up first - carbon dioxide or water?

This is a terrible question. Lets try to list down the effects of :
1. sealing the soil
2. sealing the plant
3. placing it under the sun.

1. Sealing the soil means water condensing in the outer container cannot return to the soil. Water from the soil cannot evaporate away under the sun. It also means the roots will use up the oxygen for respiration (an additional confusing factor) and will rot (an additional confusing factor).

2. Supply of carbon dioxide to the plant is limited and will be used up eventually. Sealing the plant means water vapour given out by the plant cannot escape (but also cannot return to the soil)

3. Placing the plant under the sun means light will be converted to heat inside the set-up and is trapped (greenhouse effect). Temperature inside the set-up will rise and the plant will give out more water vapour to cool down the plant. i.e. rate of transpiration will increase. However, with bright light from the sun, the rate of photosynthesis will also increase.

From the able analysis, we can see that both the rate of usage of water and carbon dioxide have increased. Therefore, to determine which is the main cause for the rate of photosynthesis to decrease, (i.e. which is used up first), the amount of water (i.e. size of the pot) and carbon dioxide available (i.e. size of the outer enclosure) will be the determining factor.

Based on my reading of the mindset of the person who set the question, I think the answer he/she wants is \"water\" because water is used for both transpiration and photosynthesis while carbon dioxide is used only for photosynthesis.

Anyway, it is a lousily set question as I can argue that the amount of water in the pot was \"so much so\" that carbon dioxide is used up first. The saddest truth is in real life, the photosynthesis will decrease not due to lack of water nor carbon dioxide. The plant will be dying because it cannot remove heat fast enough because of the intense heat inside the set-up (like the interior of a car parked under the hot sun)

PS once I bought a pot of orchid, left it in the car (under the sun) and continued shopping for less than an hour. The orchid looks fine when I reached home. I was shocked the next morning to find all the leaves had turned brown - it was just amazing.

[kittycat01]

sorry, atutor, the description is not that accurate. it’s actually in the psle science paper this year. According to my daughter, the plant is in a sealed beaker of water (no soil) but only the root part is immersed in the sealed beaker. and it’s placed under the lamp, not the sun. The rest of the details are correct. Sorry for the confusion. I should have clarified with her first before putting the question down on this forum.


Anyway, just to comment - lots of dd’s classmates put CO2 being the answer but others put water.