If you are driving 72 Km/h along a straight road and you reduce your speed to 45 km/h in 4.0 s, what is your acceleration during this inattentive period?

Explanation:

Motion With Constant Acceleration

It occurs when the velocity of an object changes uniformly in time.

The equation that rules the change of velocities is:

Where:

a   = acceleration

vo = initial speed

vf  = final speed

t    = time

Solving for a:

The initial speed is vo=72 Km/h and it's reduced to vf=45 km/h in a time of t=4 s. Both speeds will be converted to m/s:

vo=72*1000/3600 = 20 m/s

vf=45*1000/3600 = 12.5 m/s

Now calculate the acceleration:

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