Question

What is the unit of speed among the following?
$A)\text{ }m/s$
$B)\text{ }m$
$C)\text{ }s$
D) None

Answer 1

Hint: This problem can be solved by using the definition of speed in terms of the distance and time and putting the units of the physical quantities in the equation, to ultimately get the unit of speed. Speed can be defined as the ratio of the distance travelled by a body to the time period in which it travels.

Formula used:
$v=\dfrac{d}{t}$

Complete step-by-step answer:
We will use the mathematical definition of the speed of a body and put in the units of the physical quantities in the definition to get the unit of speed.
The speed $v$ of a body that covers a distance $d$ in a time period $t$ can be written as
$v=\dfrac{d}{t}$ --(1)
Now, the unit of distance is metre $\left( m \right)$.
The unit of time is second $\left( s \right)$.
Putting these two values in the equation (1), we get the unit of speed as
$\dfrac{m}{s}=m/s$
Hence, we have got the unit of speed as metre per second $\left( m/s \right)$.

So, the correct answer is “Option A”.

Note: Students must note that velocity of a body also has the same units as the velocity of a body is the ratio of the displacement of a body to the time period in which the displacement occurs. This is because displacement has the same unit as that of distance.
Students must also know that metre per second $\left( m/s \right)$ is the SI unit of speed. However, there are also other units such as centimeter per second $\left( cm/s \right)$ and kilometer per hour $\left( km/hr \right)$ that are not the SI units but used commonly in day to day life for different purposes.