1.

Two particles A and B collide to separate out. Show that their total momentum conserves.

Answer»

Let initial momenta of the particle A and B be \(\vec{p}_A\) and \(\vec{p}_B\) respectively. The particles collide and separate out with final momentum \(\vec{p}'_A\) and \(\vec{p}'_B\) respectively. Using Newton’s second law of motion, the force of on particle A due to B is given by, \(\vec{F}_{AB}=\frac{\vec{p}_{A'}-\vec{p}_A}{t}\)

Where, t is the time interval.

Similarly, \(\vec{F}_{BA}=\frac{\vec{p}'_B-\vec{p}_B}{t}\)

As per Newton’s third law of motion,

\(\vec{F}_{BA}=-\vec{F}_{BA}\)

i.e., \(\frac{\vec{p}_{A'}-\vec{p}_A}{t}\) =  \(\frac{\vec{p}'_B-\vec{p}_B}{t}\)

i.e., \(\vec{p}'_A\) + \(\vec{p}'_B\) = \(\vec{p}_A\) + \(\vec{p}_B\)

Linear momentum is conserved.



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