Q&A - PSLE Science

[mother777]

Seed–>sparrow–>snake–>eagle

Not sure this is correct, but seems ok to me…

[Mary Joy]

pls help with these food chains…


grass----->?------->?--------->Man

seed------->sparrow--------->?------------>?___

[Verysuperkiasu]

There is a science question in RGS 2012 prelim qn 37.


It’s about an experiment with 3 types of material containers containing water to be placed in a room with constant temp of 35 deg C for 3 days. Picture shows the results of experiment :
Material R container with most water, material S with least water and material T with moderate water level.

Question (a):
Based on the observations above, what can you infer about the properties of material R, S and T?
Answer : S is best conductor of heat - so heat is absorbed into the container S faster hence warmer temperature of water increases rate of evaporation. R is the poorest conductor, followed by T.

Question (b)
Ravi repeated the experiment by placing the containers in an air-conditioned room at at temperature of 20 deg C for 3 days. Would there be any difference in the change of water level in the three containers compared to the earlier experiment. Explain your answer

My question is (b) - will the air cond room reduce humidity hence dryer air increases rate of evaporation but the lower temp decreases rate of evaporation. So there will be no change in water level?

Answer key is : water level will be higher than the results in first experiment due to lower temperature of air cond. But how about the humidity factor?

[Verysuperkiasu]

There is a science question in RGS 2012 prelim qn 37.


It’s about an experiment with 3 types of material containers containing water to be placed in a room with constant temp of 35 deg C for 3 days. Picture shows the results of experiment :
Material R container with most water, material S with least water and material T with moderate water level.

Question (a):
Based on the observations above, what can you infer about the properties of material R, S and T?
Answer : S is best conductor of heat - so heat is absorbed into the container S faster hence warmer temperature of water increases rate of evaporation. R is the poorest conductor, followed by T.

Question (b)
Ravi repeated the experiment by placing the containers in an air-conditioned room at at temperature of 20 deg C for 3 days. Would there be any difference in the change of water level in the three containers compared to the earlier experiment. Explain your answer

My question is (b) - will the air cond room reduce humidity hence dryer air increases rate of evaporation but the lower temp decreases rate of evaporation. So there will be no change in water level?

Answer key is : water level will be higher than the results in first experiment due to lower temperature of air cond. But how about the humidity factor?

[SAHMwith2boys]

Need help on the following questions:


1. One of the following objects has the same energy conversion as a portable VCD player when it is used to play a movie. Which one is it?
1) Cuckoo Clock
2) Computer harddisk
3) Siren of police car
4) Oven

The answer given was (2), can someone help to explain why?

2. When in use, which of the following appliances will convert electrical energy to kinetic energy and heat energy only as useful forms of energy?
A. Blender
B. Toaster
C. Iron
D. Hair dryer

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

Answer given was (4), can someone explain why?

Thanks for the help.

[SAHMwith2boys]

http://i49.tinypic.com/14tx2me.jpg\">


Answer given was (1), can explain why?

[StudentproinMATHandScience]

SAHMwith2boys:

http://i49.tinypic.com/14tx2me.jpg\">


Answer given was (1), can explain why?

I'm a student very good in Science and actually it's quite obvious right?
Conclusions
A:Least dark
B:Less Dark
C:Mediocre dark
D:Very dark
Temperature:
A:lowest
B:2nd lowest
C:2nd highest
D:highest
From here it's quite obvious already.The darker the object is,the higher the temperature it has.Hence answer is (1)
:imcool:

[SAHMwith2boys]

StudentproinMATHandScience:

SAHMwith2boys:

http://i49.tinypic.com/14tx2me.jpg\">


Answer given was (1), can explain why?

I'm a student very good in Science and actually it's quite obvious right?
Conclusions
A:Least dark
B:Less Dark
C:Mediocre dark
D:Very dark
Temperature:
A:lowest
B:2nd lowest
C:2nd highest
D:highest
From here it's quite obvious already.The darker the object is,the higher the temperature it has.Hence answer is (1)
:imcool:

But the temp is A:lowest, B: 2nd highest, 2nd lowest and highest. So is it considered conclusive?

[Verysuperkiasu]

Does anyone know if friction depends on surface area. I mean friction between two concrete surfaces. ( I know air resistance, which is a form of friction, does indeed depend on surface area. )


I ask this question because DD’s teacher said so. But I check guide books - they only say friction depends on the texture of surface - rougher it is, more friction. That makes sense to me. But not sure about surface area though. And how about weight?

[Sun_2010]

Verysuperkiasu:

Does anyone know if friction depends on surface area. I mean friction between two concrete surfaces. ( I know air resistance, which is a form of friction, does indeed depend on surface area. )


I ask this question because DD's teacher said so. But I check guide books - they only say friction depends on the texture of surface - rougher it is, more friction. That makes sense to me. But not sure about surface area though. And how about weight?

If my memory serves me right,
Frictional force does not depend on area of contact.

Frictional force is proportional to Normal force so is proportional to weight of object .