## Welcome Back To Our Examination Paper Analysis Series!

To play a part in Singapore’s movement “Towards Zero Waste”, more Singaporeans are now bringing along their reusable bags around when they go grocery shopping.

Have you ever encountered a time when you bought too many things while grocery shopping and your reusable bag snapped because the things that you placed in the bag are just too heavy?

Unfortunately, I have…when I overzealously tried to put 10 kg of apples in my reusable bag! I had my apples rolling all over the ground when my bag snapped… 🍎

With the thought that the reusable bag that snapped was too weak, I decided to purchase another brand of reusable bag that I believe is much stronger. Without disappointment, on my next grocery shopping trip, I purchased 2 kg of biscuits, placed them in my reusable bag and VOILA! The new reusable bag did not break!

Let’s pause my story here for a quick food for thought…

🍎 Food For Thought: Was it correct to conclude that the second reusable bag was indeed stronger than the first reusable bag that snapped?

To answer this question, we will be reviewing the 2019 CHIJ St. Nicholas Girls’ School (SNGS) P6 Preliminary Examination Paper.

What I'll Be Sharing In This Article

## Let’s Get Started On This Question!

Source: CHIJ St. Nicholas Girls’ School – 2019 P6 Preliminary Examination Paper [Q20]

## Thought Process

Looking at the question, I believe you will be able to identify that this question is testing you on the concepts from the topic of Materials. Are you able to tell which property of materials is tested here?

If you are thinking of ‘strength’, you are correct!

🪙 What is strength?

Strength is the ability of the material to withstand weights without breaking.

Questions often require students to know how to identify/compare the strength of the materials given.

Do you know how to test the strength of materials?

⛓ We can test a material’s strength by placing weights on it and find out the maximum weight the material can withstand without breaking!

A stronger material withstands more weight without breaking.

A weaker material withstands less weight without breaking.

This also means that if you place a weight that is heavier than what the material can withstand on it, the material will break! After understanding what strength is, let’s first analyse the strength of rope J.

## Question Analysis

Rope J

We can see that rope J has not broken even though a 50 kg mass was hung on it. What does that tell us about the strength of rope J?

This shows that rope J is strong enough to withstand/hold at least 50 kg mass without breaking.

However, did the question state that 50 kg was the maximum weight that rope J can withstand before breaking? No!

As such, there is no information on how much more weight rope J can withstand before breaking and we cannot tell how much weight rope J can hold before breaking!

After analysing rope J, let’s take a look at rope K.

Rope K

As seen from the diagram below, rope K broke when a 150 kg mass was hung on it. This shows that rope K is not strong enough to withstand 150 kg of weights.

On top of this, we can also conclude that rope K definitely CANNOT withstand a mass that is 150 kg or more without breaking.

However, from the piece of information above, are we able to tell the maximum weight that rope K can withstand before breaking? No, it is impossible to tell!

Maybe rope K could withstand a mass of 149 kg…? Maybe rope K breaks when a mass of 1 kg was hung on it…? We cannot tell!

From the analysis that we have done for ropes J and K above, here is a summary table that depicts the range of mass that ropes J and K can/cannot hold without breaking.

 J K L M Able to hold up to 50 kg without breaking Definitely unable to hold weights that are 150 kg and above ? ? We are unable to tell the exact maximum weight each rope can hold without breaking! ? ?

With this, I would like you to try and think of the range of mass that rope L and rope M can/ cannot hold without breaking and see if it tallies with my answer below! 🙂

 J K L M Able to hold up to 50 kg without breaking Definitely unable to hold weights that are 150 kg and above Definitely unable to hold weights that are 40 kg and above Able to hold up to 150 kg without breaking We are unable to tell the exact maximum weight each rope can hold without breaking!

Now that you have understood the range of mass that each rope can/cannot hold without breaking, let’s look at the statements given in the question to find out which statement(s) is/are definitely true.

Source: CHIJ St. Nicholas Girls’ School – 2019 P6 Preliminary Examination Paper [Q20]

## Analysis Of Statement A

“Statement A: Material L is the weakest.”

Many students tend to choose statement A as one of the correct statements and this is their thought process:

“Since the mass placed on the rope made of material L is the lightest and the rope made of material L broke, this means that material L is the weakest and statement A is definitely true.”

Do you agree with the above claim? The above claim is actually… wrong! Let’s compare the rope made of material L to the other 3 ropes to find out why!

Comparing ropes made of materials L, J and M

From the above illustration, we can see that the rope made of material L cannot withstand the mass of 40 kg and broke. This is unlike the ropes made of materials J and M, which were able to withstand a mass of 50 kg and 150 kg respectively and did not break as a result. Thus, we can conclude that material L is indeed weaker than materials J and M.

Comparing ropes made of materials L and K

From the above illustration, we can see that both ropes made of materials L and K broke when a mass of 40 kg and 150 kg were placed on them respectively. But the catch here is that it is unknown which exact weight will cause material K to break.

Maybe it’s 30 kg…? Maybe it’s 145 kg…?

As such, we are unable to tell if material L or material K is the weakest of them all and statement A is not definitely true.

## Analysis Of Statement B

“Statement B: Material M is the strongest.”

Similar to statement A above, I noticed that many students also tend to choose statement B as one of the correct statements and this is their thought process:

“Since the mass placed on the rope made of material M is the heaviest and the rope made of material M did not break, this shows that material M is the strongest and statement B is also definitely true.”

Do you agree with the above claim too? The above claim is actually also… wrong! Let’s compare the rope made of material M to each of the other 3 ropes to find out why!

Comparing ropes made of materials K, L and M

From the above illustration, we can see that the rope made of material M was able to withstand a mass of 150 kg without breaking. This is unlike the ropes made of materials L and K, which cannot withstand a mass of 40 kg and 150 kg respectively and broke as a result. Thus, we can conclude that material M is indeed stronger than materials L and K.

Comparing ropes made of material J and M

From the above illustration, we can see that both ropes made of materials J and M were able to withstand a mass of 50 kg and 150 kg respectively as they did not break. But it is unknown if material J can withstand a mass of more than 150 kg without breaking.

Maybe material J can withstand 200 kg…?

Maybe material J can only withstand 100 kg…?

As such, we are unable to tell if material J or material M is the strongest of them all and statement B is not definitely true.

## Analysis Of Statement C

“Statement C: Material J is stronger than material L.”

Comparing ropes made of materials J and L

From the above illustration, we can see that material L broke even though a lighter (40 kg) mass was placed on it while material J remained unbroken even though a heavier (50 kg) mass was placed on it. Thus, we can conclude that material L is weaker than material J and statement C is definitely true.

## Analysis Of Statement D

“Statement D: Material K is weaker than material M.”

Comparing ropes made of materials K and M

From the above illustration, we can see that when the same mass of 150 kg was placed on both materials K and M, material K broke while material M did not break. This shows that material K was unable to withstand a mass of 150 kg but material M was able to withstand a mass of 150 kg. Thus, we can conclude that material K is indeed weaker than material M and statement D is definitely true.

Source: CHIJ St. Nicholas Girls’ School – 2019 P6 Preliminary Examination Paper [Q20]

Since only statements C and D are definitely true, the answer for this question is option (2).