Q&A - PSLE Science

[Muffins]

fudgemum:

Hi all,


This Nanyang SA2 Q10.

Animals such as antelope and deer live in groups. This is one of the behavioural adaptations of the animals to help them survive better in the grassy plains of Africa.

Which of the following explains how living in herds help these types of animals to increase the chances of survival on the grassy plains ?

A. Animals move together to look for food.
B.These animals, when in groups can attack their predators.
C.The animals in their own group warn each other when they sense danger and move together.
D.Predators, intimidated by their great number, will not attack them when they are in their groups.

(1) A and B only
(2) A and C only
(3) A, B and C only
(4) B, C and D only

Worksheet answer is (2). Can anyone pls explain. TIA.

Hi fudgemum, at first, you would think that the answer should include the 4th one, but look closely at the question? They will not survive only on GRASSY PLAINS only if D is included, but anywhere. B is not included because they do not usually attack their predator, rather, they run away from it....

[fudgemum]

Hi Muffins,


Thanks a lot for your reply. Yes. We were confused because of option D.

Some more clarification in the same paper.

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

1. Need an explanation for Q 24.
2. Is the answer correct for Q 30.

TIA.

[fudgemum]

Muffins:

fudgemum:

Hi all,


A. Animals move together to look for food.
B.These animals, when in groups can attack their predators.
C.The animals in their own group warn each other when they sense danger and move together.
D.Predators, intimidated by their great number, will not attack them when they are in their groups.

(1) A and B only
(2) A and C only
(3) A, B and C only
(4) B, C and D only

Worksheet answer is (2). Can anyone pls explain. TIA.

Hi fudgemum, at first, you would think that the answer should include the 4th one, but look closely at the question? They will not survive only on GRASSY PLAINS only if D is included, but anywhere. B is not included because they do not usually attack their predator, rather, they run away from it....

Hi Muffins,

Option C is also not a must for grassy plains and it can be anywhere. C is also somewhat like D. Is it because the best possible answer is 2. Thank you once again

[ruyu]

cheif think we should award tianzhu with some award for his contribution to the community

[tianzhu]

Hi fudgemum


I’ll take Q30 first. The key point here is both objects are on resting on the table. Hence option (1) is offside.

From the view from the top, we can tell that the objects are two square cubes of different sizes. Fig 2 and 3 show possible 3D pictorial shapes. I suggest you form two different cubes using Lego blocks or used boxes so that your child can see a clearer picture.

Option (4) is out as it shows the side elevation of a triangular prism and a small cube.

Option (3) is the right answer.

Best wishes


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[tianzhu]

Hi fudgemum

Good Morning

In primary science, students learnt that light travels in a straight line. When light falls on an object, some of it is reflected back.

In answering this question, I wish to give a brief introduction of some terms which may help us to understand the question better.

When light reflects from an angle, it bounces off at the same angle as it hits it. The angle of incidence is equal to the angle of reflection. The ray of light hitting the mirror is called the incident ray and the ray bouncing off is the reflected ray. The normal is a line drawn perpendicular to the shiny surface so that we can easily measure the angles.

I feel that it’s important to have a bit more understanding before we answer this question; otherwise the answering process becomes very mechanical. Don’t worry too much about the terms at this juncture; I think it’ll be covered more thoroughly in secondary one.

Now, just follow the procedures as described in the image to get the answer. As this is not the original test paper, pictures may be distorted and may not reflect the actual picture in the original test paper.

Try the same for the other 3 options, and you’ll realize that you cannot get two equal angles after drawing the perpendicular line.

The answer is option (1).Have fun.

Best wishes

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[fudgemum]

Hi tianzhu,


Thank you very much for your time. I understand your explanation for Q24.

For Q30 , just want to check with you, (i) the screen is horizontal (flat) on top of the object, right ?. (ii) the screen, object and the torch are not moved. Then how can you get B and C.

Thank you.

[tianzhu]

Hi fudgemum


A shadow is made when an opaque or translucent object blocks light. The shadow appears on the screen behind the object.

The object is between the light source and screen as shown in the question.The diagram shows the experimental set up as seen from above. Imagine standing at the overhead bridge and look down, you can see the top views of vehicles passing by.

Fig 1 shows the plan elevation or view from top of two blocks put on a table.Fig 2 and 3 are two possible 3 D pictorial shapes based on the given elevation in the question.

The blocks can be arranged in two ways as shown in fig(2) and (3).
If the blocks are arranged as in fig (2), you’ll get the shadow as shown in .If the blocks are arranged as in fig (3), you’ll get the shadow as shown in (B).Hence the answer is option (3)

Try doing this at home; get two square blocks, one big and one small one, place torchlight in front of the blocks and use the wall as screen behind the blocks.

The screen is behind the objects and for this question, there’s isn’t a need to consider the movement of the light source, objects or screen.

Hope you can understand. I am not sure if I can draw a picture out with Paint and Words. It’s pretty tedious.

If you still don’t get it, let me know. Maybe, I’ll try to do a sketch.

Best wishes

[fudgemum]

Hi tianzhu,


Thank you…Thank you…

I was thinking the screen is on top of the object (forgot about the table) and the light source below the object. So I was expecting the top view to be the shadow. In the picture all the three objects are shown one above the other.

Now I understand. The trick is to interpret the top view of the object to the fig 2 and 3.


Have a nice day. Thank you.

[Sun_2010]

tianzhu:

Hi fudgemum


I’ll take Q30 first. The key point here is both objects are on resting on the table. Hence option (1) is offside.

From the view from the top, we can tell that the objects are two square cubes of different sizes. Fig 2 and 3 show possible 3D pictorial shapes. I suggest you form two different cubes using Lego blocks or used boxes so that your child can see a clearer picture.

Option (4) is out as it shows the side elevation of a triangular prism and a small cube.

Option (3) is the right answer.

Best wishes

Thanks Tianzhu,
I was checking my ds work 2 days back on this paper, and was surprised to see the answer in the sheet was given as 4 (B, C and D), but you are right it cant be.

And i was breaking my head wondering if the square is the base of a prism , if so how can it stand on a tip - sigh going crazy!