PSLE 2012 - Science

[RVHS]

ultimateschooler:

The force of friction is a force acting from a surface in the opposing direction of the body's tendency to slide. It is due to both the normal force pushing from a surface against a body and a condition of the surface called the coefficient of friction. Dependent on whether the body is at rest or moving there is a different coefficient of friction. Static friction is used when the body is at rest and is defined by

Ffriction=Nμs

where Ffriction is the force of Friction, N is the normal force, and μs is the coefficient of static friction. Kinetic friction is used when the body is sliding along the surface and is defined by
Ffriction=Nμk
where μk is the coefficient of kinetic friction

The force of friction is a force acting from a surface in the opposing direction of the body's tendency to slide[/color]
if someone try to push but box still stationary, then there is friction
so for A, no friction as no push or pull force.

[charsen]

Hi

I am back.Overall,the paper was quite ok.The booklet A was quite tricky but it is easy to solve once you know the topic and concept.Booklet B,hmm,a lot of explanation questions.I took a long time for the mist question.I like that kind of question as it is an application question.I wish all the best to all those who are having their higher mother tongue.
For those who have completed their PSLE like me,congratulations! Letd have a goooooooooooooood break for all the hardwork we’ve done

Charsen

[charsen]

RVHS:

ultimateschooler:

The force of friction is a force acting from a surface in the opposing direction of the body's tendency to slide. It is due to both the normal force pushing from a surface against a body and a condition of the surface called the coefficient of friction. Dependent on whether the body is at rest or moving there is a different coefficient of friction. Static friction is used when the body is at rest and is defined by

Ffriction=Nμs

where Ffriction is the force of Friction, N is the normal force, and μs is the coefficient of static friction. Kinetic friction is used when the body is sliding along the surface and is defined by
Ffriction=Nμk
where μk is the coefficient of kinetic friction

The force of friction is a force acting from a surface in the opposing direction of the body's tendency to slide[/color]
if someone try to push but box still stationary, then there is friction
so for A, no friction as no push or pull force.

Hi
There is friction when the object is in contact in the ground.Known as static friction.Not sure of this question,but since there is static friction,there is friction acting on the object.
Charsen

[Ontheballmother]

One more qn - pl help. Something like that - cant recall actual qn.

What is the diff between mammals and birds?
A) bird has wings
B) there are body covering

Tks in advance.

[Haneyi]

Ontheballmother:

One more qn - pl help. Something like that - cant recall actual qn.

What is the diff between mammals and birds?
A) bird has wings
B) there are body covering

Tks in advance.

Hello,
I put body covering as the answer.

Birds -> Feathers
Mammals -> Fur / hair

Hope this helps. ^^

[sammifan]

BeContented:

kiasu学生:

[quote=\"BeContented\"]DS also say different from usual. Section A - ok. Section B - tough.

Face dun look very optimistic, dun even want to say much

All he remembered was
'Adult frog live on land & tadpoles in water. State 2 advantages for it'.
:yikes:

Hi BeContented, just did ppr, the 2 advantages is that:
1: they do not have to compete for water, food and space.
2: when the frog habitate is destroyeed, the tadpole r not living in the same habitat as frog and thus will survive 2 grow into frgs, ensuring continuity of their own kind.

im p6 too!!
i put
no need to compete for food.
young will not be eaten by adult. So right??

You the GOOD !! :rahrah:
Told my son & he went 'oh yah!! Why din I think of that (2)!
So I guess it's really applying what one knows. Not something kids dun know, just can't link.
Thanks very much.[/quote]

[Ontheballmother]

Haneyi:

Ontheballmother:

One more qn - pl help. Something like that - cant recall actual qn.

What is the diff between mammals and birds?
A) bird has wings
B) there are body covering

Tks in advance.

Hello,
I put body covering as the answer.

Birds -> Feathers
Mammals -> Fur / hair

Hope this helps. ^^

Thanks! My ds too :imcool:

[Ares23]

Newton’s first law states that a body at rest will remain at rest and a boy in constant uniform motion in a straight line will remain in a constant uniform motion in a straight unless a net force acts on the body. In this case, friction is the resistive force. Thus, if the box is stationary, even if there is a push, that means there is no net force acting on the body as f=ma due to friction.

[sammifan]

hi. i put that too!! correct?? n u said "U THE GOOD’’ to the person who said compete for food?

[sammifan]

thesjarox:

vaidyanathan padmini:

How about friction question from McQ.....

My dd's answer is only C as friction opposes motion...
Only the box in c is moving so it should have friction

Confirmed with teacher-A,B and C.
Friction also acts on stationary objects. That's why forces have to overcome the friction before being able to move the object. Also, if there were no friction acting on an object,the object would glide across the surface, like ice, and would never stop.
Thus, A is also correct.

no trust me only b n c r correct.. BUT IT WAS STILL FLAT ON THE SURFACE