This problem is solved by the equation of motion:
x = x0 + v0*t + 1/2*a*t^2,
Here x0 = 0, v0 = 40ft/sec and a = -5 ft/s^2, we need to solve for t:
v = v0 + a*t, solve how long does it take to stop: 0 = v0 + a*t --> a*t = -v0 --> t = -v0/a
-- > 40/5 = 8 seconds to stop.
In this time, the car travels x = 0 + 40*8 + 0.5*-5*8^2 ft ~ 160 ft.
Answer: The car travels 160 ft.
