For my answer to the question above, Let's assume that there is no friction.
The total energy E (kinetic + potential) of the tire is:
E = mv^2 / 2 + mgh
Since we're not given the tire's mass distribution or the hill's coefficient of friction or anything, assume we're to disregard rotational inertia, the energy dissipated as heat, etc.
Given that:
m = 10.0 kg
v0 = 2.0 m/s
h0 = 20.0 m
We're to find v when h = 5.0 m
Since the overall energy is conserved,
m(v0)^2 / 2 + mg(h0) = mv^2 / 2 + mgh
=>
v = sqrt((v0)^2 + 2g(h0 - h)
= sqrt( 4.0 m^2 / s^2 + (2)(9.8 m / s^2) (15.0 m) )
= sqrt( 298 m^2 / s^2 )
= 17.26 m/s
