Understanding the Basic Unit of Speed

The question asks about the basic unit of speed of an object. Speed is a measure of how fast an object is moving. It is defined as the distance traveled by an object per unit of time. Mathematically, speed can be expressed as:

Speed = \(\frac{\text{Distance}}{\text{Time}}\)

SI Units for Distance and Time

In physics and science, we commonly use the International System of Units (SI units). The SI system provides a standard set of units for various physical quantities. To find the basic unit of speed, we need to consider the basic SI units for distance and time.

• The basic SI unit of distance or length is the metre (m).
• The basic SI unit of time is the second (s).

Deriving the Basic Unit of Speed

Since speed is calculated by dividing distance by time, the basic SI unit of speed is obtained by dividing the basic SI unit of distance by the basic SI unit of time.

Basic Unit of Speed =  \(\frac{\text{Basic Unit of Distance}}{\text{Basic Unit of Time}}\) =  \(\frac{\text{metre}}{\text{second}}\)

This unit is written as metre per second and abbreviated as m/s.

Analyzing the Options

Let's look at the given options:

• metre per km (m/km): This unit does not represent speed correctly because 'km' is a unit of distance, not time. It would be distance per distance, which doesn't fit the definition of speed.
• metre per hour (m/h): This unit represents speed (distance per time), but 'hour' is not the basic SI unit of time. While it is a valid unit for speed, it's not the *basic* SI unit.
• metre per second (m/s): This unit represents speed (distance per time), and 'metre' is the basic SI unit of distance, and 'second' is the basic SI unit of time. This is the standard basic unit of speed in the SI system.
• metre per minute (m/m): This unit represents speed (distance per time), but 'minute' is not the basic SI unit of time. While it is a valid unit for speed, it's not the *basic* SI unit.

Therefore, the basic unit of speed of an object in the SI system is metre per second (m/s).

Conclusion on Basic Speed Unit

Based on the definition of speed as distance over time and using the basic SI units for distance (metre) and time (second), the basic unit of speed is metre per second (m/s).

Revision Table: Key Physics Concepts

Additional Information on Units of Speed

While metre per second (m/s) is the basic SI unit, speed can be expressed in many other units depending on the context and system of measurement. Some common units include:

• Kilometre per hour (km/h): Often used for car speeds. \(1 \text{ km/h} = \frac{1000 \text{ m}}{3600 \text{ s}} = \frac{5}{18} \text{ m/s}\).
• Miles per hour (mph): Used in countries following the imperial system. \(1 \text{ mph} \approx 0.447 \text{ m/s}\).
• Centimetre per second (cm/s): Part of the CGS (Centimetre-Gram-Second) system. \(1 \text{ m/s} = 100 \text{ cm/s}\).
• Knots: Used for nautical and aeronautical speeds. \(1 \text{ knot} = 1 \text{ nautical mile per hour} \approx 0.514 \text{ m/s}\).

The term "basic unit" usually refers to the unit derived directly from the base units of the chosen system (like SI). In the SI system, metre (m) and second (s) are base units, making m/s the basic derived unit for speed.