I am trying to calculate the average force with regards to this question:
Calculate the average force that USA gold medalist Allyson Felix (mass = $55.3$ kg, height = $168$ cm) exerted backwards on the track to accelerate from $0$ to $10.2\, m/s$ over $25 \,m$, if she encountered a headwind that exerted an average force of $10.0\,N$ against her.
The answer is correct but I'm a little stuck. Where is the value 2.08 coming from? How do I get this value?
Working: By
$v^2 = u^2 + 2as$
$(10.20)^2 = 0 + 2a\cdot (25)$
$a = 2.08 \,m/s^2$
Thus by $F = ma = (55.30) \cdot (2.08) = 115.10 \,N$
$F_{total} = 115.10 + 10 = 125.10 \, N$
Showing more work, note that: \begin{align*} (10.20)^2 &= 0^2 + 2a\cdot (25) \\ (10.20)^2 &= 50a \\ a &= \dfrac{(10.20)^2}{50} = 2.0808 \\ \end{align*} Rounding to three significant figures, we obtain $a = 2.08 ~ m/s^2$.