Question

list all the derivations of physics class 9th cbse.

Answer 1

Chapter 8 : Motion
1. Derivation of unit of acceleration
2. Derivation of three equations of motion by graphical as well as mathematical method
(a). v= u+at
(b). s =ut +1/2 at^2
(c). 2as = v^2 - u^2

Chapter 9 : Force and laws of motion
1. Derivation of second law of motion i.e F =ma
2. Derive first law pf motion through second law of motion.
3. Derive third law of motion through second law.
4. Conservation of momentum 's derivation.

Chapter 10 : Gravitation
1.Universal law of gravitation
2. Unit of gravitational law
3. Prove that f =mg
4. Derive W = m×g

Chapter 11 : Work and energy
1. Derivation of kinetic energy
2. Derivation of potential energy
3. Derivation of conservation of energy
4. Commercial unit of energy.

Answer 2

1. v=u+at
we know, a = v-u/t
                at = v-u
                v = u+at
2. s=ut+1/2at^2
We know, s = Average v X t
Average v = (u+v)/2
.:  s = (u+v)/2 X t                   eq.(1)

Again we know that:
v = u + at
substituting this value of “v” in eq.(1), we get

    s = (u+u+at)/2 x t
=>s = (2u+at)/2 X t
=>s = (2ut+at^2)/2
=>s = 2ut/2 + at^2/2

or s = ut +1/2 at^2

3. v^2 = u^2 +2as

We know that
     v = u + at
=> v-u = at
or t = (v-u)/a                                 eq.(1)

Also we know that
   s = average v X t
.: s = [(v+u)/2] X [(v-u)/a]                    from above
=> s = (v^2 – u^2)/2a

=>2as = v^2 – u^2

or v^2 = u^2 + 2as

Hope this helps.