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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.

Answer :

it is corecct becasue it 10 s more added from 0.05
migueletorallam

Answer:

He is incorrect!  Her speed was 5m/s.

Explanation:

For calculating the speed, first we shall remember that:

[tex]v=\dfrac{d}{t}[/tex]

Where [tex]v[/tex] is the speed, [tex]d[/tex] is the distance travelled and, [tex]t[/tex] is the time it takes to travel distance [tex]d[/tex].

So one migth think that velocity can be easely compute:

[tex]v=\dfrac{0.05}{10}[/tex]

[tex]v=0.005\dfrac{m}{s}[/tex]

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

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

[tex]d=0.05km[/tex], distances is measure in Kilometers.

[tex]t=10s[/tex], time is measure in seconds.

If we want our speed to be in [tex]m/s[/tex], 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

[tex]0.05Km=50m[/tex],

now we can compute the speed:

[tex]v=\dfrac{d}{t}[/tex]

[tex]v=\dfrac{50m}{10s}[/tex]

[tex]v=\5dfrac{m}{s}[/tex]

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