Q&A - PSLE Science

[OliverNg]

can anyone explain why the answer is (4)? Thank you!

[jojoberry]

Hui Ying hung two objects x and y on two identical springs. Which one of the following statements correctly explains why spring B is longer than spring A after the objects are hung on them?
(Object x is hung on spring A and object y is on spring B)

1) the mass of object y is more than that of object x.
2) spring A stretches less than spring B for the same amount of mass.
3) the elastic spring force acting on object y is less than that acting on object x.
4) the gravitational force acting on object x is less than that acting on object y.

Ans given is 1. Can the answer be 4? Tia

Answer cannot be 4, gravitational force experienced by all objects are the same. Their weight is affected by the mass.

[jojoberry]

can anyone explain why the answer is (4)? Thank you!

Conditions required for photosynthesis - presence of carbon dioxide, water and sunlight.

while A has no water vapour, it gets the water from the roots.
In B, the lack of carbon dioxide will prevent photosynthesis.
In C, the availability of carbon dioxide will allow photosynthesis
In D, oxygen helps respiration, but it also can photosynthesize as carbon dioxide is produced during respiration.

[bestwishes]

Hui Ying hung two objects x and y on two identical springs. Which one of the following statements correctly explains why spring B is longer than spring A after the objects are hung on them?
(Object x is hung on spring A and object y is on spring B)

1) the mass of object y is more than that of object x.
2) spring A stretches less than spring B for the same amount of mass.
3) the elastic spring force acting on object y is less than that acting on object x.
4) the gravitational force acting on object x is less than that acting on object y.

Ans given is 1. Can the answer be 4? Tia

Answer cannot be 4, gravitational force experienced by all objects are the same. Their weight is affected by the mass.

I think there is a confusion in the use of terms gravitational force (mg) and gravitational field strength (g).

[guchengyouzi]

I think should stress more on the force than the mass

[guchengyouzi]

can anyone explain why the answer is (4)? Thank you!

Conditions required for photosynthesis - presence of carbon dioxide, water and sunlight.

while A has no water vapour, it gets the water from the roots.
In B, the lack of carbon dioxide will prevent photosynthesis.
In C, the availability of carbon dioxide will allow photosynthesis
In D, oxygen helps respiration, but it also can photosynthesize as carbon dioxide is produced during respiration.

I don't understand the D part.
In the first place, what did the plant burn to respire in the first place.
As I see it, the plant had to burn starch to produce carbon dioxide during respiration.
Then it used up carbon dioxide to produce starch during photosynthesis.
It is a zero sum game. Nothing is gain.

[guchengyouzi]

I need help with this. It's under the topic of energy.



a. Heat energy comes from underground - geothermal energy
b. When cold water from the tank travels down the pipe, it gains heat from the ground and becomes warm. The warm water then returns to the hot water storage tank (it is less dense than cold water and rises).
c. it is a renewable source of energy
d. then the room temperature is the same temperature as the underground

Is it a renewable energy?
What is heating up the underground?
Would the heating be there forever?

[guchengyouzi]

Hi, need help with these 2 questions.

1. When we exercise, our rate of breathing increases. The advantage of increasing the rate of breathing is to ____________.
1) have faster exchange of gases
2) allow blood to flow through the lungs more quickly
3) decrease the amount of water vapour in the blood
4) allow blood to flow to the small intestine more quickly for increased absorption of digested nutrients

2.Which of the following advances in science and technology have a positive impact on our environment?
a. improved breeding methods for plants and animals
b. deforestation to clear land for construction of buildings
c. new recycling methods for materials, such as papers, metals and plastics
d. new farming methods with decreased use of chemical insecticides or pesticides

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

1. 1 is the best answer, though admittedly not as complete as what the open ended questions would demand (they'll probably penalise for not writing what gases they are etc.). 2 is to achieve 1, so if they asked for two answers I would pick 2 as well. 3 doesn't make sense, water does not exist as vapour in the blood, and even if it did it not related to the question. 4 we're talking about breathing and exercising not digestion, so it can't possibly be an advantage. In fact, when you exercise more blood is diverted away from the digestive system.

2. Best answer is 3: A, C and D. A is a bit ambiguous, I mean, improved breeding methods doesn't always mean it's good (e.g. improved methods of cutting down trees). I guess with the benefit of doubt, we can give it to A, since there isn't an option for C and D only anyway. B is deforestation, obviously bad by primary school syllabus standards. C and D are phrased so positively (decreased use of pesticides, new recycling methods), it must be good!

I think only gaseous exchange will do.
Making blood flowing faster through lungs depends on heart rate, beats per minute.

[guchengyouzi]

Dear Science expert!

please help this question.

Qn:
Shalome likes to jump on her spring mattress as it lifts her up in the air as shown below. (As attached)

Imagine she jumps on solid ground, each jump would reach the same height.
But now there is spring in the mattress.
The spring would retain her previous height.
On top of that, she exerts the force of her next jump.

[guchengyouzi]

One of the question in the Science Booklet B PSLE Paper 2014 consisted of a string and a load hanged at the tip of the string until the string breaks. First string : 45 units of weights needed, and the other one I forgot. The question (a) asked what property ( I forgot what word ) they were testing on.

My answer : The elasticity of the string

My friends : The strength of the string.

I always thought that whenever the experiment tests for strength, weights would be placed in the middle of the string until it breaks? Someone please tell me whether my answer is wrong or correct. Thanks!

This is what I know. Does the question state how long the string extended when the weight is hang? If hv, then it is testing for elasticity. But the question state until the string break, then it is testing for strength. Definition of strength is the ability to withstand load without breaking. Definition of elasticity is the ability to stretch.

Technically, it is tensile strength.