Question

How can we get 3 law from 2 law of motion

Answer 1

Derivation of Newton’s third law of motion from Newton’s second law of motion Consider an isolated system of two bodies A & B mutually interacting with each other, provided there is no external force acting on the system. Let FAB,be the force exerted on body B by body A and FBAbe the force exerted by body B on A. Suppose that due to these forces FABand FBA, dp1/dt and dp2/dt be the rate of the change of momentum of these bodies respectively. Then, FBA=dp1dt ---------- (i) => FAB=dp2dt ---------- (ii) Adding equations (i) and (ii), we get, FBA+ FAB=dp1dt+ dp2dt ⇒ FBA+ FAB=d(p1+p2)dt If no external force acts on the system, then d(p1+p2)dt = 0 ⇒ FBA+ FAB= 0 ⇒ FBA= - FAB---------- (iii) the above equation (iii)represents the Newton's third law of motion (i.e., for every action there is equal and opposite reaction)...