Q&A - PSLE Science

[Garfieldpal]

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 .

Sun_2010 is correct. Frictional force does NOT depend on the surface area in contact. Rather, it depends on the weight or mass of the object.

[Alanyklim]

Thx

[clblinym]

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This is from RGS 2012 Sa1 Q25
Can anybod here explain why the answer given is 3. TIA. Amy

[clblinym]

http://i49.tinypic.com/2mfnion.png\">

Another one is from Rosyth 2001 SA1 Q8.

The answer given is 2. Can anybody explain why? Many thanks. Amy

[zinc6539]

clblinym:

http://i49.tinypic.com/14shc9h.jpg\">

This is from RGS 2012 Sa1 Q25
Can anybod here explain why the answer given is 3. TIA. Amy

You can observe from the graph that every 50g increase in weight causes the spring to become 10cm longer. The question also states that the relationship is proportionate until 200g. Therefore:

50g - 20cm
100g - 30cm
150g - 40cm

[tomotom0]

Hello can anyone help me with this Q?

The answer given is (3), why isn't it (1)?

The ball bearing should drop very quickly from (1) to (4) due to gravity right?
Like, since at (1), the GPE is at maximum, the GPE would be converted to KE, so it should move the fastest at (1)?

Thanks in advance!

http://i1352.photobucket.com/albums/q659/tomotom0/92d0b24f-973a-44ef-aa33-8ababa9007f1_zps2dd895e3.jpg\">

[Sun_2010]

tomotom0:

Hello can anyone help me with this Q?

The answer given is (3), why isn't it (1)?

The ball bearing should drop very quickly from (1) to (4) due to gravity right?
Like, since at (1), the GPE is at maximum, the GPE would be converted to KE, so it should move the fastest at (1)?
Precisely.
GPE is max at 1 and min at 3.
What happened to the GPE ? It got converted into KE.
Where is KE max ? at 3
So where is it fastest - at 3

Thanks in advance!

[Mary Joy]

Hello everyone,

Pls help me with this science question related to adaptations.....Thanks

1.What is the feature of a water boatman?
The function of this feature:To 'row' through water

2.What are animals that have streamined body shape(excluding sharks)?

3.What are the functions of the wings and claws of the chicken?

4.What are the functions of the beak and claws of the eagle?

5.What are 2 similarities between a bird's wings and the planes's wings?And how does these similarities help the plane to fly?

[Laura02]

atutor2001:

SAHMwith2boys:

Hi all, need help with the following question:


Which of the following objects are not affected by gravitational force?
A. A bird flying in the sky
B. A man lying on the floor
C. A balloon rising into the sky

1. B only
2. A and C only
3. A and B only
4. None of the above

The answer given was (3), but couldn't understand why??

The answer should be (4) because if there is no gravitational force acting on the objects :
A. A bird flying in the sky can stay in the sky without flapping its wings
B. A main lying on the floor can be lifted up with our little finger.
C. A balloon rising into the sky need not be filled with a light gas but can be filled with stone and by give an upward push, it will continue to rise.

I think the question is ambiguous. By definition, gravitational force is the force of attraction between all masses in the universe; especially the attraction of the earth's mass for bodies near its surface; \"the more remote the body the less the gravity\". So gravitational forces are acting in all 3 of the above scenarios (a, b & c). By the question is weather they are \"affected\" by gravitational forces. In a & c, the forces created by \"lift\" is greater than the forces of gravity... I think.

[Laura02]

clblinym:

http://i49.tinypic.com/2mfnion.png\">

Another one is from Rosyth 2001 SA1 Q8.

The answer given is 2. Can anybody explain why? Many thanks. Amy

This is the same principle as why greenhouses work, isn't it?

\"A greenhouse works by taking in sunlight and heating it up. This process is the conversion of solar energy (sunlight) to thermal energy (heat). Greenhouses are designed to allow sunlight to filter through the walls and ceiling. The sunlight warms the trapped air inside, creating chemical reactions. These reactions help the plants to grow to their full capacity while protecting them from outside elements \" quoted from e-how.