A truck covers 40.0 m in 7.10 s while smoothly slowing down to a final velocity of 2.75 m/s ... (a) Find the truck's original speed.

D = vo t - at²/2

v = vo - at

40 m = vo · 7.10 - a · (7.10) ²/2

40 m = 7.10 vo - a· 50.41/2

40 m = 7.10 vo - 25.205 a

2.75 m/s = vo - 7.10 a ⇒ a = (vo - 2.75) / 7.10

40 = 7.10 vo - 25.205 · (vo - 2.75) / 7.10

40 = 7.1 vo - 3.55 vo + 9.7625

3.55 vo = 30.2375

vo = 30.2375 : 3.55 = 8.5176 m/s

Answer: the truck's original speed is 8.5176 m/s.