The car observer measured initial energy as 0.5*5*6*6 Joules = 90 J and final energy as 0.5*5*(-3)*(-3) + 0.5*30*(+1.5)*(+1.5) Joules = 56.25J with a loss of Joules. The sidewalk pedestrian observer reported an initial energy of 0.5*5*(+4)*(+4) + 0.5*30*(-2)*(-2) = 100 J and final energy as 0.5*5*(-5)*(-5) + 0.5*30*(-0.5)*（-0.5） = 66.25J with a loss of Joules. The arithmetic showed that the total kinetic energy loss to heat, sound, etc. of the two-object system (impactor-target system) is the s for both observers, just like the exchange impulse of 45 N-sec is the s for both observers.