Question

What do you mean by fundamental & derived quantities? Give the derived unit of Linear momentum (P).

Answer 1

Hint: Fundamental quantities are mass, time, current, length, temperature, amount of substance and luminous intensity. All other physical quantities are derived quantities and can be made from fundamental quantities. Momentum is the product of mass and velocity.

Complete Step By Step Solution:
Fundamental quantities are the basic or base quantities. These are independent of each other. They consist of the quantities which are essential to form all other physical quantities apart from fundamental quantities. Derived quantities are the quantities which are formed with the help of fundamental quantities. All fundamental quantities with their units are:
- Mass(kg)
- Length(m)
- Time(s)
- Current(A)
- Temperature(K)
- Amount of substance (mol)
- Luminous intensity (cd)

All other quantities and their units can be derived by some combination of these fundamental quantities. For e.g.
Charge \[q=it\] , unit of charge As
Momentum is the product of mass and velocity and is represented by p
\[P=mv\]
It's S.I. unit will be a product of S.I. unit of mass and velocity i.e.
$kgm{{s}^{-1}}$

Additional Information:
Rate of change of momentum is called force. Also if net force on a system or a body is zero then its momentum remains conserved. This principle is known as the law of conservation of momentum.

Note: One of the mistakes which student commits is that they often consider charge as a fundamental quantity and current as a derived quantity but as per the convention current is the fundamental quantity and charge is derived from it.
$q=it$
$C=As$
All fundamental quantities must be remembered as it can be used in question and will always be, not provided.