Question

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 1

it is corecct becasue it 10 s more added from 0.05

Answer 2

He is incorrect! Her speed was 5m/s.

Step-by-step explanation:

For calculating the speed, first we shall remember that:

`v=(d)/(t)`

Where
`v` is the speed,
`d` is the distance travelled and,
`t` is the time it takes to travel distance
`d`.

So one migth think that velocity can be easely compute:

`v=(0.05)/(10)`

`v=0.005(m)/(s)`

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

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

`d=0.05km`, distances is measure in Kilometers.

`t=10s`, time is measure in seconds.

If we want our speed to be in
`m/s`, 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

`0.05Km=50m`,

now we can compute the speed:

`v=(d)/(t)`

`v=(50m)/(10s)`

`v=\5dfrac{m}{s}`