Given
m1 = 15kg
vi1 = +20 m/s
vf1 = +5 m/s
m2 = 10 kg
vi2= -15 m/s
vf2 = ?
Procedure
Conservation of momentum, general law of physics according to which the quantity called momentum that characterizes motion never changes in an isolated collection of objects; that is, the total momentum of a system remains constant.

The speed of the 10kg Ball is 7.5m/s
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Here is an example on the usage of ellipsis:
I don't know . . . i'm not even sure how i feel about him.
The dots acted as an interlude that connected one response with another statement</span>
Answer:
V = I(R+r)
Explanation:
According to ohms law, the current (I) passing through a metallic conductor at constant temperature is directly proportional to the potential difference (V) across its end.
Mathematically, V= IR where V is the potential difference
I is the current
R is resistance
Given emf (E) = IRt... (1)
where E is the emf
Rt is the total equivalent resistance
The external resistance Rv is connected in series with the internal resistance 'r' to give total equivalent resistance Rt = (R+r)
Substituting in equation 1
E = I(R+r)
The equivalent potential difference V = I(R+r)
Together as one moving package, their mass is (15 + 50) = 65 kg.
Kinetic energy = (1/2) (mass) (speed)²
= (1/2) (65 kg) (5 m/s)²
= (32.5 kg) (25 m²/s²)
= 812.5 kg-m²/s² = 812.5 joules .