Answer :
The way I look at these things is like this:
-- The runner covered 12 meters in 4 seconds.
Average speed = 3 meters per second.
-- Speed at the beginning = zero.
In order to make the average 3, Speed at the end = 6 meters per second.
-- Speed increased from zero to 6 meters per second in 4 seconds.
It must have increased 1.5 meters per second each second.
That's choice-#2.
-- The runner covered 12 meters in 4 seconds.
Average speed = 3 meters per second.
-- Speed at the beginning = zero.
In order to make the average 3, Speed at the end = 6 meters per second.
-- Speed increased from zero to 6 meters per second in 4 seconds.
It must have increased 1.5 meters per second each second.
That's choice-#2.
Here we have -
Acceleration (a) = ?
Initial velocity (u) = 0 m/s (runner starts from rest)
Distance (s) = 12 m
Time (t) = 4 seconds
So, using the second equation of motion, we have-
[tex]s = ut + \frac{1}{2}at^{2} [/tex]
[tex]12 = 0*4 + \frac{1}{2}*a*4 ^{2} [/tex]
[tex]12 = 0+8a[/tex]
[tex] \frac{12}{8} = a[/tex]
[tex]1.5m/ s^{2} [/tex]
So, option (2) is correct.
Acceleration (a) = ?
Initial velocity (u) = 0 m/s (runner starts from rest)
Distance (s) = 12 m
Time (t) = 4 seconds
So, using the second equation of motion, we have-
[tex]s = ut + \frac{1}{2}at^{2} [/tex]
[tex]12 = 0*4 + \frac{1}{2}*a*4 ^{2} [/tex]
[tex]12 = 0+8a[/tex]
[tex] \frac{12}{8} = a[/tex]
[tex]1.5m/ s^{2} [/tex]
So, option (2) is correct.