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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?


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 v0 = 100 km/h = 28m/s, the final velocity is v0 = 0, and the displacement is x = 55 m.

From the kinematics equation v2 = v02 + 2ax, finding a:

a = (v2 - v02)/2x = [0 - (28m/s)2]/(2x55m) = - 7.1 m/s2.

The necessary force is then:

F = ma = (1500 kg)(-7.1m/s2) - 1.1x104 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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