Question

Sarah backstrokes at an average speed of $8$ meters per second how long it would take her to complete a race of $200\,m$?

Answer 1

The average speed of a body in a certain time interval is the total distance covered by the body in that time interval divided by the time interval so if a particle covers a certain distance $s$ in a time$t$ then the average velocity is given by ${V_{av}} = \dfrac{s}{t}$. We have distance and average speed is given and we have to calculate the time interval taken by Sarah to cover the given distance.

Complete step by step answer:
Here we have given average speed, and the total distance covered by Sarah in some interval of time and we have to calculate that time interval. Now as we have given that,
Distance travelled Sarah, $s = 200m$
Average speed of Sarah, ${V_{av}} = 8m/s$
Time travelled by Sarah to cover that distance, $t = ?$
From the formula of average speed we have, ${V_{av}} = \dfrac{s}{t}$
By changing the sides of average velocity and time in order to obtain the time we have
$t = \dfrac{s}{{{V_{av}}}}$
Substituting the values given, we get;
$t = \dfrac{{200}}{8}s$
On doing simple division we get
$\therefore t = 25\,s$

Hence Sarah will take 25 seconds to backstroke the race of 200 m at an average speed of 8meters per second.

Note: The question might be differ by changing the magnitudes of the quantity. Also there might be change in the unit of measurement like there could be km/h instead of m/s for creating misjudgement. One should also know the difference between average speed and the average velocity in order to solve similar questions in linear line. Average velocity is the total displacement divided by the total time taken.