Question

Question 5.17 A nucleus is at rest in the laboratory frame of reference. Show that if it disintegrates into two smaller nuclei the products must move in opposite directions.

Chapter Laws Of Motion Page 111

Answer 1

Nucleus is at rest initially,
e.g u = 0
Initial linear momentum = mu = 0
Let the nucleus disintegrates into two parts having mass m1 and m2 with speed v1 and v2 respectively.

Change in momentum after disintegration = m1v1 + m2v2
Here , external force = 0
According to law of conservation ,
Pi = Pf
0 = m1v1 + m2v2
V2 = -(m1/m2)V1

Here negative sign indicates that v1 and v2 are in opposite directions .

Answer 2

Explanation:

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