# Math Help - which Equations constant I use here ?

1. ## which Equations constant I use here ?

Hi ALL

which Equations constant I use here ?

a truck covers a distance of 50 m in 8 s while smoothly sowing down to a final speed of 2.5 m/s . find its original speed

Dx = 50 m
t = 8 s
v = 2.5 m/s

Now I take this equation bit I don't now why I didn't get the correct answer

Dx = (v + v0 ) t/2

=50 = 2.5 + v0 ) 8 /2
=2 X 50 + 92.5 + v0 ) 8 /2
=100 = 20 + 8v0/2
=128v
v = -128

2. but here in my book the answe is 10 m/s
??

they do v0 = 2DX/2-v = 2 X 50 /8 -2.5 = 10
??please I want the help beacuse I fell confused
I wait

3. sorry ... forgot the 8 seconds

$50 = \frac{1}{2}(v_0 + 2.5) \cdot 8$

$50 = 4(v_0 + 2.5)$

$\frac{25}{2} = v_0 + 2.5$

$v_0 = 10$