posted by Scott on .
A red car and a green car, identical except for color, move toward each other in adjacent lanes and parallel to an x-axis. At time t=0, the red car is at x sub r = 0 and the green car is at x sub g = 220m. If the red car has a constant velocity of 20km/h, the cars pass each other at x = 44.5m, and if it has a constant velocity of 40 km/h, they pass each other at x=76.6m. What are (a) the initial velocity and (b) the constant acceleration of the green car?
Use the two distances to calculate how long it takes then to pass each other.
For Vr = 20 km/h = 5.555 m/s, they pass after 44.5/5.555 = 8.01 seconds. At that time, the green car has traveled 220 - 44.5 = 175.5 m
For Vr = 40 km/h = 11.111 m/s, they pass after 76.6/11.111 = 6.894 s. at that time, the green car has traveled 220 - 76.6 = 143.4 m
Finally using those times and the corresponding distances traveled by the green car, solve two equations in two unknowns for Vo and a of the green car.
That step I leave up to you.
Thanks a bunch!