A63.0-kg sprinter starts a race with an acceleration of 4.20 m/s2 . what is the net external force on him?

From Newton's second law of motion, it was stated that the net external force on a certain object can be calculated by multiplying its mass to the acceleration. This can mathematically be expressed as,
     Fnet = m x a
where m is mass and a is acceleration.

Substitute the known values to the equation,
      Fnet = (63 kg) x (4.20 m/s²)
      Fnet = 264.6 kg m/s²
 
ANSWER: Fnet = 264.6 N