Brad is working on a speed problem in physics class. the problem tells him that a girl runs from her house to the park 0.05 km away in 10 s. brad calculates that her speed is 0.005 m/s. is he correct? if not, explain the flaw or flaws in his problem solving process.

He is incorrect!  Her speed was 5m/s.

Explanation:

For calculating the speed, first we shall remember that:

Where is the speed, is the distance travelled and, is the time it takes to travel distance .

So one migth think that velocity can be easely compute:

Be carefull, he does not make a proper dimensional analisis!  

Before computing the speed we must know in what dimensions our values are.

, distances is measure in Kilometers.

, time is measure in seconds.

If we want our speed to be in , first we need to be sure that our values are expressed  in meters and seconds.

Time is already  expressed in seconds, distance is not in Kilometers.

So

,

now we can compute the speed:

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