Q&A - PSLE Science

[Cheerfuldad]

Verysuperkiasu:

atutor2001:

Hi Verysuperkiasu


The shadow on the screen depends on the relative distances between the objects and also the distance of the light source from the small square. Below are some of the scenarios :

1. Light source is very close to small square and the ball is quite a distance from the small square - shadow will be that of the small square

2. Light source is very close to small square and the ball is also very close to small square - shadow will be that of the ball.

3. Light source is a distance from small square and ball very close to small square and big square is a distance from the ball - shadow will be that of the ball.

...... and so on.

The only way to find out is to draw light rays from the light source on the actual picture and see which object blocks the light rays. That object will give the shadow.

Thanks....unfortunately my son didn't notice the distance and he can't remember now. It was today's science mcq question. He put 'square' as the answer.

Logically if u see from the front, since the length of the square is the same as the diameter of the circle, then you should see a square because of this four right angle corners. But u have a point about the relative distance though. Think my son overlooked that factor.

But the question given is the side profile. Can he still draw lines to find out if the ball indeed blocks the square? Because the 4 corners cannot be seen from the side profile?

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.

[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'.

[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...