Revision 3

Revision Questions (5 to 8)

Question 5

1. An object thrown in the air came to a stop and fell back to the ground. Explain the phenomenon, considering the forces acting on the object. (2)

When an object is thrown upwards, an upward force is applied initially. As it rises, gravity acts downward, opposing the motion. Its velocity decreases until it stops momentarily at the highest point, then falls back due to gravity pulling it downward.

2. Amit measured the length of his science project display with a piece of string, and then used a ruler to find the string's length. He found the display to be 2 metres long. Why is this not an accurate method of measuring length? (3)

The method is not accurate because the string may not be held straight, it can stretch or shrink, and errors can occur while transferring the measurement to the ruler. A rigid measuring scale gives more accurate results than a flexible string.

3. Give five examples of elements. What is the difference between elements and compounds? (2)

Examples of elements: Oxygen, Hydrogen, Iron, Gold, Carbon.
Difference: An element is made up of only one kind of atom, while a compound is made of two or more elements chemically combined in fixed proportions.

4. Write down two ways in which friction can be reduced. (2)

1. By applying lubricants like oil or grease between surfaces.
2. By using ball bearings or smooth surfaces to reduce contact.

Question 6

1. Define the area of a surface. Calculate the area of a triangle with a base length of 15 cm and a height of 20 cm. (4)

Area of a surface: It is the total space occupied by the boundary of a plane figure.
For a triangle: Area = ½ × base × height = ½ × 15 × 20 = 150 cm².

2. Write two ways in which the friction of a surface can be increased. (2)

1. By roughening the surface.
2. By using materials with higher grip, like rubber soles.

3. Water can exist in all three states of matter. Which of these states has the least density and why? (2)

Water vapour (gas) has the least density because its particles are far apart and free to move, occupying more volume.

4. Stretching a string can change its shape. Explain whether it is a solid or another state of matter. (2)

A string is a solid. Solids have a definite shape but can change shape under force (elasticity). Stretching temporarily changes its shape but it remains a solid.

Question 7

1. Does a gas occupy space? If yes, give examples. (2)

Yes, gas occupies space. Example: Air fills a balloon or a tyre, proving that gases occupy the container’s volume.

2. Compare the states of matter based on the movement of their particles. (2)

In solids, particles vibrate in fixed positions.
In liquids, particles move freely but remain close together.
In gases, particles move randomly and rapidly in all directions.

3. Can you use a ruler with a worn-out zero marking? List precautions while measuring objects. (4)

No, a ruler with worn-out zero cannot be used accurately as it causes zero error.
Precautions:
1. Place object close to zero mark.
2. Keep eye perpendicular to scale.
3. Avoid parallax error.
4. Use a ruler with clear, accurate markings.

4. Mention the conventions for writing units and their symbols. (2)

Units are written in singular form (e.g., metre not metres).
Symbols are written in lowercase without a full stop (e.g., m for metre, kg for kilogram).

Question 8

1. Define static and rolling friction. (2)

Static friction: Force that prevents an object from starting to move.
Rolling friction: Resistance when an object rolls over a surface.

2. An eraser gets smaller with use. Give reasons. (2)

Due to friction between paper and eraser, small particles of the eraser wear off, making it smaller with use.

3. Aeroplanes are streamlined like a bird. Give reasons. (2)

Streamlined shape reduces air resistance (drag) and allows smooth airflow, making flight more efficient, just like in birds.

4. Will the effect of friction be larger when a heavy object is moved or when a lighter object is moved? (2)

The effect of friction is larger when moving a heavy object because friction depends on the normal force, which increases with weight.

5. List 5 units used for measuring length. (2)

Metre (m), Centimetre (cm), Millimetre (mm), Kilometre (km), Micrometre (µm).