Question

What is the SI unit of speed?

Answer 1

- Hint: You can easily find the SI unit of speed by using the units of Distance and Time in MKS system.

Complete step-by-step solution -

SI unit of Speed can be derived with the help of distance and time. Basically, speed is the scalar equivalent of velocity. Mathematically speed is given as the ratio of distance to the time taken.
\(v=\dfrac{distance}{time}\) ϑ=dt
Where,
d is the distance measured using SI unit of distance; that is meter.
t is the time interval measured using the SI unit of time; that is seconds.
Here, we can see that length and time are base quantities, thus we can say that speed can be measured with the SI unit of length (meters) over the SI unit of time (seconds). Or in other words, to derive SI units of velocity or speed we will simply substitute corresponding units in the formula of velocity.
\(SI\;unit\;of\;Speed=\dfrac{meter}{second}\)

Hence, the SI Unit of speed is meter per second or m/s or $m.s^{-1}$.
Dimensional Formula of speed is $M^0.L^1.T^{-1}$

ADDITIONAL INFORMATION:
Difference between speed and velocity
Speed denotes only how fast an object is moving, whereas velocity describes both how fast and in which direction the object is moving. If a car is said to travel at 60 km/h, its speed has been specified. However, if the car is said to move at 60 km/h to the north, its velocity has now been specified.
The big difference can be discerned when considering movement around a circle. When something moves in a circular path and returns to its starting point, its average velocity is zero, but its average speed is found by dividing the circumference of the circle by the time taken to move around the circle. This is because the average velocity is calculated by considering only the displacement between the starting and end points, whereas the average speed considers only the total distance travelled.
Units of speed include:
metres per second (symbol m/s), the SI derived unit;
kilometres per hour (symbol km/h);
miles per hour (symbol mi/h or mph);
knots (nautical miles per hour, symbol kn or kt);
feet per second (symbol fps or ft/s);
Mach number (dimensionless), speed divided by the speed of sound;
In natural units (dimensionless), speed divided by the speed of light in vacuum (symbol c = 299792458 m/s).

Note:- The SI base units are the standard units of measurement defined by the International System of Units (SI) for the seven base quantities of what is now known as the International System of Quantities. The units and their physical quantities are the second for time, the meter for measurement of length, the kilogram for mass, the ampere for electric current, the Kelvin for temperature, the mole for amount of substance, and the candela for luminous intensity. The SI base units are a fundamental part of modern metrology, and thus part of the foundation of modern science and technology.
One can easily form SI units of any physical quantity using these seven fundamental base units.