Q&A - PSLE Science

[Michaelia0816]

I have a question which I am unsure of,


Do pond skaters eats plants ( like algae)?

[Michaelia0816]

Pls help,

http://t.co/q9WybVC6

Is the answer 2?

[elkniwt]

Hi,


Like to check if mushrooms are micro-organisms?

The links below seem to indicate they are :
http://archives.microbeworld.org/microbes/fungi/

But aren't micro-organisms microscopic? :?

Asked this based on this qn from RGS :
http://i47.tinypic.com/e83mn5.jpg\">

TIA.

[Robertpattinsonidle]

pls help me with this question. http://i49.tinypic.com/29qb05w.jpg\">

[Robertpattinsonidle]

http://i46.tinypic.com/xp37uf.jpg\"> pls help.

[verykiasu2010]

the answer should be ‘b’


it is impossible for ‘c’ to happen because it is impossible to retain the same brightness or to achieve reflection from infinite distance (the line plateauing means it is reflected from infinite distance, which is impossible).

the reflection must end at some distance because the further the light source is, the more the light will be dispersed along the way, hence eventually zero light reflected

[Robertpattinsonidle]

verykiasu2010:

the answer should be 'b'


it is impossible for 'c' to happen because it is impossible to retain the same brightness or to achieve reflection from infinite distance (the line plateauing means it is reflected from infinite distance, which is impossible).

the reflection must end at some distance because the further the light source is, the more the light will be dispersed along the way, hence eventually zero light reflected

thank u. anyways... the answer key says A. any explanation why?

[Sun_2010]

I no science teacher but i think the question is incomplete unless the units of the x axis is given.


If one unit is 100m then B is best.
If one unit is 1000m then is A better as the cyclist need not be seen 4 km away.
If one unit is 10m then A or B will not be sufficient, 40 m will be too short to react.

[verykiasu2010]

Robertpattinsonidle:

verykiasu2010:

the answer should be 'b'


it is impossible for 'c' to happen because it is impossible to retain the same brightness or to achieve reflection from infinite distance (the line plateauing means it is reflected from infinite distance, which is impossible).

the reflection must end at some distance because the further the light source is, the more the light will be dispersed along the way, hence eventually zero light reflected

thank u. anyways... the answer key says A. any explanation why?

I think your teacher is correct

the one who gave the answer for the answer key probably read the graph but has the thinking process in the opposite, misinterpreted the info : shorter distance represented by the graph means the light stopped being reflected at that short distance - meaning it won't reflect anymore after that distance and hence not a good material for safety vest - which has to be as reflective as possible. the answer giver may be thought shorter distance needed to reflect light, hence is better. This is not the case

for 'b' it is able to have the light reflected at a longer distance, meaning more visible from longer distance than 'a', hence better material for safety vest.

p.s.
edited with more explanation

[verykiasu2010]

Sun_2010:

I no science teacher but i think the question is incomplete unless the units of the x axis is given.


If one unit is 100m then B is best.
If one unit is 1000m then is A better as the cyclist need not be seen 4 km away.
If one unit is 10m then A or B will not be sufficient, 40 m will be too short to react.

no need distance in units lah, the length represented by 'a', 'b', 'c' are clearly different, so will not be mistaken in the diagram