Question

Express the speed 36 \[km{{h}^{-1}}\text{ in }m{{s}^{-1}}\].
A) 3600 \[m{{s}^{-1}}\]
B) 10\[m{{s}^{-1}}\]
C) 0.6 \[m{{s}^{-1}}\]
D) 36 \[m{{s}^{-1}}\]

Answer 1

Hint: We need to understand the relation between the basic units used for the physical quantities such as the speed, distance and time to find the required solution for this problem. The given unit can be converted to the required unit easily (here, \[m{{s}^{-1}}\]).

Complete Solution:
We are given a system which travels with a given speed which is expressed in the units of kilometers per hour. We know that the speed is the measure of how fast or slow a body moves with the given reference frame.

Speed is defined as the rate of change of the distance. It is expressed as the distance travelled to the time taken. Like, any other physical quantity, the speed also has units which are used appropriately in situations to give a precise idea of the situation.

The speeds of automobiles are usually expressed in kilometers per hour or miles per hour, whereas the speed of a man walking can be better expressed in meters per second.

The standard international unit used for speed is the meters per second. It is used because it can give the idea of the speed of any body from huge aeroplanes to the motion of electrons with some sense in the reader.

We can convert from one form to another, here from 36 \[km{{h}^{-1}}\text{ to }m{{s}^{-1}}\] as follows –
\[\begin{align}
  & v=36\dfrac{km}{hr} \\
 & \Rightarrow v=36\dfrac{1000m}{3600s} \\
 & \therefore v=10m{{s}^{-1}} \\
\end{align}\]
So, the speed 36\[km{{h}^{-1}}\] is equal to 10 \[m{{s}^{-1}}\].

The correct answer is option B.

Note:
The speed of any body is a relative quantity. We consider the surrounding to be the reference frame which is at rest so as to get the absolute value of the speed of the body. The unit of speed whether relative or absolute will remain the same as it conveys the same idea.