The two different isotopes have weights :
w1 = 78.918 amu
w2 = 80.916 amu
average weight w3 = 79.903 amu
The mixing of two components can be modeled as
let the fraction of w1 be 'x'
hence 
now this is a linear equation in 'x'. Substituting the values we get
x = 0.507
hence the percentage of Br79 = 50.7% and the percentage of BR81 = 49.3%
I hope it is clearly visible.. Velocity of the center of mass of 2-ball system is - 11.54m/s. Minus indicates, velocity direction is in downward direction.
Answer:
a) 567J
b) 283.5J
c)850.5J
Explanation:
The expression for the translational kinetic energy is,

Substitute,
14kg for m
9m/s for v

The translational kinetic energy of the center of mass is 567J
(B)
The expression for the rotational kinetic energy is,

The expression for the moment of inertia of the cylinder is,

The expression for angular velocity is,

substitute
1/2mr² for I
and vr for w
in equation for rotational kinetic energy as follows:



The rotational kinetic energy of the center of mass is 283.5J
(c)
The expression for the total energy is,

substitute 567J for E(r) and 283.5J for E(R)

The total energy of the cylinder is 850.5J