# physics

posted by Ted

Starting from the constant-acceleration kinematic equations, write a formula that gives xf in terms of t, xi, vf, and a.

1. Damon

Huh ?
in terms of vf?????

2. Sam

yes in terms of vf. we are asked to combine different kinematic equations to drive xf. I believe the equation v=vo+at^2 can sub for vo. does this make sense?

3. Damon

v = Vi + a t
vf = Vi + a T so Vi = vf-aT

x = xi + Vi t + (1/2) a t^2
xf = xi +(vf-aT)t + (1/2) a t^2
if t = T final time
xf = xi + vf T - a T^2 + (1/2) a T^2

xf = xi + vf t - (1/2) a t^2

ok, it just changes the sign of the at^2 term
(It still uses the AVERAGE speed during the interval !!)

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