Without using law of conservation of linear momentum, prove newton's tird law ON NUMERICAL OR THEORETICAL BASIS(NOT EXPERIMENTAL BASIS i.e. based on real life examples).

Asked by DIVYANSHU VADEHRA | 9th Dec, 2013, 10:21: AM

Expert Answer:

Consider two bodies of mass m1 and m2
 
Their total momentum is P = P1 + P2
 
Now, the net force from Newton's second law is given as
 
F = dP/dt = dP1/dt + dP2/dt
 
Now, at the time of contact (this is needed so that third law becomes applicable) no net force acts on the system.
 
Thus,
dP1/dt + dP2/dt = 0
 
f1 + f2 = 0
 
Thus, f1 = -f2
 
This is Newton's third law.

Answered by Romal Bhansali | 10th Dec, 2013, 10:36: AM

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