# Net External Force on a Sprinter| Newton’s Second Law of Motion: Concept of a System| Dynamics| College Physics| Problem 4.1

### A 63.0-kg sprinter starts a race with an acceleration of 4.20 m/s2. What is the net external force on him?

SOLUTION:

From Newton’s Second Law of Motion, the net external force on a body is equal to the product of its mass and acceleration. Therefore,

$\sum \:F=ma$

$\sum \:F=\left(63.0\:kg\right)\left(4.20\:m/s^2\right)$

$\sum \:F=264.6\:kg\cdot m/s^2$

$\sum \:F=264.6\:N$

The net external force on the sprinter is $264.6\:Newtons$