Question

horse and dog are running with the same speed. one of them has more kinetic energy than other why?

Answer 1

kinetic energy = 1/2 * m v²
m = mass ,    v = speed

If the horse and dog have the same speed at a point of time, then they may have different KE due to different  masses (or weights).

If the horse has more weight, then its KE is more.

Answer 2

kinetic energy depend upon speed of moving body and mass of that body .
we know ,
mass of horse > mass of dog
given,
speed of horse =speed of dog
take square both side
(speed of horse )^2 =(speed of dog)^2

hence,
we see here kinetic energy depend only on mass of body { e.g horse and dog }

hence,
kinetic energy of horse is greater than kinetic energy of dog