Here’s question on Mass that was posted by a parent on our Parent Support Group.** **

Your child needs to know how to link the concepts from Mass and **Energy** to tackle these questions accurately.

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In this article, I will break down the thought process to show you how we analyse this question & you can share this with your child if you find this helpful.

## Question

## Thought Process

The four balls are of the same size and volume but are made of different materials.

As copper and iron are denser than styrofoam and paper, the mass of the copper (W) and iron (Z) ball will be larger than the styrofoam (X) and paper (Y) ball.

Hence, this suggests that Statement B, “Ball W has a greater mass than Ball X“ is correct.

The four balls in the diagram share the same cross-sectional area, therefore the air resistance acting on the balls are the same.

As such, the four balls will reach the sand at the same time.

Therefore, this shows that **S**tatement C, “All the balls will reach the sand at the same time” is correct.

Based on this line of thought, we can also safely eliminate Statement A, “Ball Y will reach the sand *first*” and Statement D, “*Ball W and Z will reach the sand before Ball X and Y*“.

### Note:

The concept of “Density” is not tested at the PSLE level.

However, students are required to recognise that different materials have different densities.

Therefore, different objects with the same volume, may weigh more than others because of different densities.

## Final Answer

The final answer is Option (2) – Statements B and C are correct!

I hope that this article has shown you the right thought process needed to tackle questions that test concepts from both Mass and **Energy** and how to arrive at the correct answer!

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