physics help!?

Question

Two cars are traveling along a straight-line in the same direction, the lead car at 25.0 m/s and the other car at 33.0 m/s. At the moment the cars are 40.0 m apart, the lead driver applies the brakes, causing his car to have an acceleration of -1.90 m/s2.

(a) How much time does it take for the lead car to stop?
-----------s
(b) Assuming that the chasing car brakes at the same time as the lead car, what must be the chasing car's minimum negative acceleration so as not to hit the lead car?
--------m/s2
(c) How much time does it take for the chasing car to stop?
----------s

I am completely lost here, can someone please explain or at least help me in getting started off? Thanks so much!

Answer 1

(a)From initial speed to complete stop:
v = at
t = v/a = 25/1.90 = 13.1579sec
(b)First find the distance for lead car:
s = (1/2)at^2 = (1/2)(1.9) (13.1579)^2 = 164.474m
Trailing car allowed distance:
40 + 164.474 = 204.474m
Assuming uniform deceleration, trailing car average speed:
v(avg) = (v(zero) + v(f))/2 = (33 + 0)/2 = 16.5m/s
Time for trailing car to stop(this is part(c))
t = D/r = 204.474/16.5 = 12.392sec
Required deceleration for trailing car:(We know it's negative)
v = at
a = v/t = 33/12.392
a = -2.663m/s

Answer 2

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