# Kinetic energy of a Tesla model S discrepancy

According to Tesla, the model S weighs 1961 kg and uses 237.5 watt hours (855000 Joules) to drive one km. However, when I plug this amount of energy and 1000 meters into the formula W=FD, I get the maximum weight that would work to be 87 kg! I am a little confused as to how an almost 2000 kg car can drive 1km with on only 237 watt hours! Here is my work

W=FD 855000 ={X KG x 9.81 m/s2} (1000 m) X=87.15 kg

According to this formula, to drive a 1961 kg car one km, i would need 19237410 Joules, a much larger amount of energy than what Tesla claims it uses! My only guess is that this has to do with an object in motion staying in motion (Newtown's 1st law). I'm very confused. I would appreciate if anyone can shed some light on this for me. My physics professor was stumped on this too. thank you!

• You're getting in the right direction, but the formula still is not right. You can estimate the friction on the tires as [friction coefficient] x [mass of the car] x [gravity of the Earth], so your answer should contain a factor of $g = 9.81...$ somewhere. See for instance hyperphysics.phy-astr.gsu.edu/hbase/mechanics/frictire.html Air resistance is more complicated and depends on the velocity $v$ of the car. – Hans Moleman Jul 1 '16 at 20:04