What net external force is required to accelerate a 155kg automobile form rest to a speed of 100km/hr in 10 seconds?

Force = (mass) x (acceleration)

The mass is easy ... it's 155 kg.

The acceleration isn't so easy, mainly because of the units.
In order to get a force in newtons, the acceleration has to be in m/s².
That will take some work.

Acceleration = (change of speed) / time = (100 km/hr) / (10 sec).

(100 km/hr) x (1,000 m/km) x (1 hour / 3,600 sec) = 1000/36  m/s

Acceleration = (1000/36 m/s) / (10sec) = (100/36)  m/s²

Force = (mass) x (acceleration) =

           (155 kg) x (100/36 m/s²) =

                     15,500/36  kg-m/s²  =  430 and 5/9 newtons =

                                               about  96.9 pounds.

(That's not much force ... mainly because your car only weighs
about 342 pounds.)

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