Density Grade 9 IGCSE Questions | PDF - Free Printable

Let's solve each question step by step:

---

Question 1:

Blessy has some cubes of material. She wants to calculate the density of one of these cubes.

#### a) Describe how she finds the mass of the cube.
To find the mass of the cube, Blessy can use a balance or scale. Here are the steps:
1. Place the cube on the balance.
2. Ensure the balance is zeroed (calibrated) before placing the cube.
3. Read the mass displayed on the balance.

#### b) What is the other physical quantity that Blessy needs to measure?
The other physical quantity needed to calculate density is the volume of the cube.

#### ii) How does she find this physical quantity?
To find the volume of the cube:
1. Measure the length of one side of the cube using a ruler or caliper.
2. Since the cube has equal sides, the volume \( V \) can be calculated using the formula:
\[
V = \text{side}^3
\]
For example, if the side length is \( s \), then:
\[
V = s^3
\]

---

Question 2:

The density of gold is 19.3 g/cm³. What is the mass of 10 cm³ gold?

The formula for density is:
\[
\text{Density} = \frac{\text{Mass}}{\text{Volume}}
\]
Rearranging for mass:
\[
\text{Mass} = \text{Density} \times \text{Volume}
\]
Given:
- Density of gold = 19.3 g/cm³
- Volume = 10 cm³

Substitute the values:
\[
\text{Mass} = 19.3 \, \text{g/cm}^3 \times 10 \, \text{cm}^3 = 193 \, \text{g}
\]

Answer:
\[
\boxed{193 \, \text{g}}
\]

---

Question 3:

What is the mass of a copper cube of side 2 cm? (Density of copper = 9 g/cm³)

#### Step 1: Calculate the volume of the cube.
The side length of the cube is 2 cm. The volume \( V \) is:
\[
V = \text{side}^3 = 2^3 = 8 \, \text{cm}^3
\]

#### Step 2: Use the density formula to find the mass.
The formula for mass is:
\[
\text{Mass} = \text{Density} \times \text{Volume}
\]
Given:
- Density of copper = 9 g/cm³
- Volume = 8 cm³

Substitute the values:
\[
\text{Mass} = 9 \, \text{g/cm}^3 \times 8 \, \text{cm}^3 = 72 \, \text{g}
\]

Answer:
\[
\boxed{72 \, \text{g}}
\]

---

Question 4:

What is density?

Density is defined as the mass per unit volume of a substance. It is a measure of how tightly packed the particles of a material are. Mathematically, it is expressed as:
\[
\text{Density} = \frac{\text{Mass}}{\text{Volume}}
\]

Answer:
\[
\boxed{\text{Density is the mass per unit volume of a substance.}}
\]

---

Question 5:

What is the SI unit of density?

The SI unit of mass is kilograms (kg), and the SI unit of volume is cubic meters (m³). Therefore, the SI unit of density is:
\[
\text{kg/m}^3
\]

Answer:
\[
\boxed{\text{kg/m}^3}
\]

---

Question 6:

How to measure the density of an irregularly shaped object?

To measure the density of an irregularly shaped object, follow these steps:

1. Measure the mass of the object:
- Use a balance or scale to determine the mass of the object.

2. Measure the volume of the object:
- Use the water displacement method:
- Fill a graduated cylinder with a known volume of water.
- Record the initial volume of water.
- Gently submerge the irregularly shaped object in the water.
- Record the new volume of water.
- The volume of the object is the difference between the final and initial volumes of water:
\[
\text{Volume of object} = \text{Final volume} - \text{Initial volume}
\]

3. Calculate the density:
- Use the formula:
\[
\text{Density} = \frac{\text{Mass}}{\text{Volume}}
\]

Answer:
\[
\boxed{\text{Use a balance to measure mass and the water displacement method to measure volume. Then, calculate density using } \text{Density} = \frac{\text{Mass}}{\text{Volume}}.}
\]

---

Final Answers:

1. a) Use a balance to measure mass.
b) Volume; measure it using \( V = \text{side}^3 \).
2. \(\boxed{193 \, \text{g}}\)
3. \(\boxed{72 \, \text{g}}\)
4. \(\boxed{\text{Density is the mass per unit volume of a substance.}}\)
5. \(\boxed{\text{kg/m}^3}\)
6. \(\boxed{\text{Use a balance to measure mass and the water displacement method to measure volume. Then, calculate density using } \text{Density} = \frac{\text{Mass}}{\text{Volume}}.}\)