Question
A long distance runner is running at a constant speed of 5 m/s. How long does it take the runner to travel 1 km.
Answer
It will take the runner 200 s to travel 1 km.
Explanation
Data: The information from the question
The runner has a constant speed, s = 5 m/s
Distance covered by the runner, x = 1 km
By converting kilometre to metre, we will have our distance (x) as:
1 km = 1000 m
Thus, distance, x = 1000 m
Unknown: The information we need to find from the question
The time it takes the runner to travel 1 km, t = ?
Formula: The equation that will help us to solve the problem
We already know that speed (s) = distance (x) / time (t)
Since we are looking for time, we will make t subject of the formula:
t = x / s [This is the equation that will help us to solve the problem]
Solution
First (simple) Method: In second
Applying t=x/s, we will have:
Time, t = x / s = 1000 m / 5 ms-1 = 200 s
Therefore, it will take the runner 200 seconds to travel 1 kilometre.
Second (alternative) Method: In hour
Since we already have our distance x = 1 km
Our speed, s = 5 m/s
We can convert the above speed into kilometres per hour (km/h) by following the method below:
Since the speed s = 5 m/s and 1 m/s = 3.6 km/h
We can equally say that s = 5 m/s = 5 (3.6 km/h) = 18 km/h
In kilometres, the speed, s = 18 kilometres per hour
Now, to find time, t = x / s = (1 km) / (18 kmh-1) = 0.06 hours.
Therefore, it will take the runner 0.06 hours to travel 1 km.
Check University Physics and Fundamentals of Physics for more examples.
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