### Solution:

Concept:A scalar quantity, such as speed, only possesses magnitude and not direction. We are aware that a speed is the transformation of a distance into a time. Speed obviously relies on time. Then, based on time, we can divide speed into average speed and instantaneous speed.

We are aware that speed equals distance times time and represents the change in distance with regard to time.

Average speed is expressed as the change in distance d over time t.

${u}_{\mathit{avg}}=\frac{d}{t}$

In contrast, instantaneous speed is the short distance travelled in a brief amount of time. Calculus is used to denote it, and it is presented as

${u}_{\mathit{inst}}=\frac{\mathit{ds}}{\mathit{dt}}$

Given that, we can conclude that a=26m/s and u=0 are the cheetah's acceleration from rest.

It goes without saying that we must determine the cheetah's travel distance in order to determine average speed.

Let t=1s represent the length of time during which the average velocity is maintained.

The distance travelled during time t by can be calculated using the second law of motion.

$s=\mathit{ut}+\frac{1}{2}a{t}^{2}$

$s=0\times 1+\frac{1}{2}\times 26\times 1\times 1=13m$

Average speed =$\frac{13}{1}$= 13 m/s

Hence, the correct option is 1.