Wonderful! The 2nd EOM says that $$s = u*t + \frac{1}{2}*a*t^2$$. We know that $$u = 0, \, t = 5$$ and $$a = -10$$. We can thus find $$s$$.
You are walking on the road. You start from rest and achieve a speed of $$20 \, \mathrm{m/s}$$ in $$4 \, \mathrm{s}$$. Which of the following would you use to determine your acceleration?
1st EOM: $$v = u + a*t$$. 3rd EOM: $$v^2 = u^2 + 2*a*s$$
• 1st EOM with $$u = 0 \,\mathrm{m/s}$$, $$v = 20 \,\mathrm{m/s}$$ and $$t = 4 \, \mathrm{s}$$
• 2nd EOM with $$u = 0 \mathrm{m/s}$$, $$t = 4 \, \mathrm{s}$$ and $$a = 10 \mathrm{m/s^2}$$
• 3rd EOM with $$u = 0 \, \mathrm{m/s}$$, $$t = 4 \, \mathrm{s}$$ and $$v = 20 \, \mathrm{m/s}$$
• 1st EOM with $$v = 0 \, \mathrm{m/s}$$, $$u = 20 \, \mathrm{m/s}$$ and $$t = 4 \, \mathrm{s}$$