a car weighs 100kg and has Velocity 0. it accelerates and its speed become 10m/s. its kinetic energy would be 100*10*10/2=5000j.
from another view car is at rest and the world accelerates and has now 10m/s speed.
as energy must be constant it should be:5000=10*10/2*(world mass except car) world mass except car=100kg?
am i using conservation of energy in wrong way, or i cant have that point of view?
The kinetic energy you determine objects to have depends on what reference frame you're in. Therefore, there's no problem here.
Energy is dependent on the coordinate frame, so in one frame the car has $E=5000J$ and in another it has $E=0$, nothing wrong about it! This is because energy is not a scalar but a component of a vector, the momentum 4-vector
$$p^\mu=(E, \vec p)$$
It transforms with a Lorentz matrix, like the coordinate 4-vector.
