Question

why second law of motion is know as real law of motion and also derive 1st and 3rd law of motion with the help of 2nd law of motion◆◆◆◆

Answer 1

SECOND LAW OF MOTION:

                                              RATE of Change of MOMENTUM is DIRECTLY Propotional  to the FORCE Applied Externally.

                                              F  α   dp/dt         ; p is the momentum

                                             

• This implies the FIRST LAW:    F α (dv/dt) m       ;       m is the mass

                                                            F = ma

                                       IF THE FORCE ACTING "F" =0

                                                 0= m*a  

                                       MASS "m" IS CONSTANT

                                                 0=m*0

Thus it implies that:

                                 " AN BODY TENDS TO BE IN REST OR MOTION UNTILL AN EXTERNAL FORCE ACTS ON IT" .

• It implies the THIRD LAW:   F(A on B) = (dv/dt)m

                                                       F(B on A)=(dv/dt)m

By ADDing the both Forces ;

                                               F(A on B) + F(B on A)= (dv/dt)m + (dv/dt)m      

                                                                                 = (dv/dt) (m+m)  

                               With no External Force the ACCELARATION =0 ( or ) the       VELOCITY IS CONSTANT.

=>                                        (dv/dt)  =  0

                                                       F(A on B)+ F(A on B)  = 0*m    

                                                       F(A on B )= -F(A on B)                                                              

                                                       

Thus the FIRST LAW OF MOTION IS CLEAR THAT ":

                                                        "    Every action has an equal and opposite reaction".

                                             

                   

Answer 2

$\orange{hey\:mate}$
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Newton's second law of motion can be used to drive both first as well as the law of motion, and hence, it is called the 'real law of motion..
1. 1st law from 2nd law
  According to 2nd law, F = ma
  If F = 0,
  ... ma = 0
  Since mass cannot be zero,  ... a = 0 
  which is 1st law.

2.  3rd Law from 2nd law
  Consider an isolated system of two bodies A and B.
  Let them collide, During collision let body A exert a force F1 on body B for time dt and let body B exert a force F2 on body for the same time dt.

  We know dp = F x t  (Impulse - Momentum Theorem)
  p2-p1 = F x t
  Now Change in linear momentum of A = F2 x dt and change in linear momentum of B = F1 x dt

As no external force is acting therfore from the law of conservation of linear momentum
  F1 x dt + F2 x dt = 0

  F1 x dt = - F2 x dt

  ...   F1 = - F2 
  which is Newton's 3rd law.....
ɪᴍᴩᴜʟꜱᴇ ᴍᴏᴍᴇɴᴛᴜᴍ ᴛʜᴇᴏʀᴀᴍ......
The impulse-momentum theorem states that the change in momentum of an object equals the impulse applied to it.

J = Δp

If mass is constant, then...

F̅Δt = mΔv

If mass is changing, then…

F dt = m dv + v dm

The impulse-momentum theorem is logically equivalent to Newton's second law of motion (the force law
➖➖➖➖➖➖➖➖➖➖➖➖➖➖➖
⏬⏬⏬ᴏʀ⏬⏬⏬
According to impulse momentum theorem,

J (Impulse) = Pf ( Fimal Momentum) - Pi( Initial Momentum) = Change in momentum

Impulse is equal to change in momentum.
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$\orange{hope\:it\:helps}$