Question

A 1451 kg car is traveling at 48.0 km/h. How much kinetic energy does it possess? K.E. =

Answer 1

           Kinetic energy  =  (1/2) (mass) (speed)²

BUT . . . in order to use this equation just the way it's written,
the speed has to be in meters per second.  So we'll have to
make that conversion.

        KE  =  (1/2) · (1,451 kg) · (48 km/hr)² · (1000 m/km)² · (1 hr/3,600 sec)²

               =  (725.5) · (48 · 1000 · 1 / 3,600)²  (kg) · (km·m·hr / hr·km·sec)²

               =  (725.5) · ( 40/3 )²  ·  ( kg·m² / sec²)

               =    128,978  joules  (rounded)