Question

Two cars pass each other traveling at the same speed. One car has a constant velocity of 18.0 m/s east. The other car has a constant acceleration of 3.00 m/s^2, west. How much time will have elapsed until the cars are 128 m apart?

Answer 1

s1=v•t
s2= v•t+a•t²/2
180= s1+s2 = v•t +v•t+a•t²/2=2 v•t+a•t²/2
a•t² +4 v•t -360 = 0
3 t²+72t-360 =0
t²+24t-120 =0
1= -12±sqrt(144+120)
t=4.25 s.