**Newton's Second Law Example
Net Force Calculation Using a Kinematics Equation.**

**What net force is needed to uniformly stop
an automobile whose mass is 1500 kg, from a velocity of 100 km/h to rest,
on a distance of 55 m?**

**Solution:**

**To use F = ma, the acceleration should be
calculated first. It is assumed that the movement is along the +x axis. The
initial velocity is v _{0} = 100 km/h = 28m/s, the final velocity is
v_{0} = 0, and the displacement is x = 55 m.**

**From the kinematics equation v ^{2}
= v_{0}^{2} + 2ax, finding a:**

**a = (v ^{2} - v_{0}^{2})/2x
= [0 - (28m/s)^{2}]/(2x55m) = - 7.1 m/s^{2}.**

**The necessary force is then:**

**F = ma = (1500 kg)(-7.1m/s ^{2})
- 1.1x10^{4} N, acting in the -x sense.**

**Newton's Second Law Links:**

** Second Newton's Law, Theory and Examples
Second Newton's Law Examples, Part Two**

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