Kenny, who has a mass of 15 kg, slides down a friction-less slide that is 3.2 m tall. cartman, who has a mass of 85 kg, slides down the same slide.
a. what speed does kenny reach at the bottom of the slide?
b. what speed does cartman reach the bottom of the slide?
c. kyle slides down the same slide. what speed does kyle reach at the bottom of the slide? explain.

a).
Kenny's potential energy at the top becomes kinetic energy at the bottom.
                          
                                               (M G H) = 1/2 (M V²)

Divide each side by 'M':                 G H = 1/2  V²

Multiply each side by  2:              2 G H = V²

Take the square root of each side:    V = √(G H)

                                                             = √(9.8 x 3.2) = 5.6 m/s .

b).
Notice in the solution for a). that each side of the equation was divided
by 'M'.  The answer didn't depend on Kenny's mass, and it doesn't depend
on Cartman's mass either.  Cartman and Kenny are both moving at the
same speed when they reach the bottom.

c).
Notice in the solution for a). that each side of the equation was divided
by 'M'.  The answer didn't depend on Kenny's mass.  It didn't depend on
Cartman's mass either, and it doesn't depend on Kyle's mass either, either. 
Each of them is moving at the same speed when he reaches the bottom.
The same also applies to girls as well, too.