Particles moving in a straight line

[phospho]

A car moving with uniform acceleration along a straight level road, passed points A and B when moving with speed 6m s−1 and 14m s−1 respectively. Find the speed of the car at the instant that it passed C, the mid-point of AB.


My working:

acceleration from AB: v = u + at, 14-6 = at, 8/t = a

distance from AB is:

s=((u+v)/2)t
s =(6+14/2)t
s = 5t

as C is the midpoint of AB, s/2 = (5/2)t = AC

so using u = 6, s = (5/2)t, a = 8/t, v = ?

v^2 = u^2 + 2as
v^2 = 36 + 2((8/t))((5/2)t)
v^2 = 36 + 40
v^2 = 76, v = 2root19, which is wrong

any ideas?

 

[TSny]

s=((u+v)/2)t
s =(6+14/2)t
s = 5t

Hi, phospho. Recheck the calculation for the steps shown above.

 

[phospho]

Hi, phospho. Recheck the calculation for the steps shown above.

eek, thanks.