Question

Can someone help with number 4 please

Answer 1

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-

$s = ut + \frac{1}{2}at^{2}$

$12 = 0*4 + \frac{1}{2}*a*4 ^{2}$

$12 = 0+8a$

$\frac{12}{8} = a$

$1.5m/ s^{2}$

So, option (2) is correct.

Answer 2

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.