How to begin this physic problem......

Question

how long does it take an automobile traveling in the left lane of a highway at 50.00 km/h to overtake (become even with) another car that is traveling in the right lane at 30 km/h when the cars' bumpers are initially 125 m apart.

the four tires of an automobile are inflated to a gauge pressure 1.9e5 Pa. each tire has an area of 0.022m^2 in contact with the ground. determine the weight of the automobile.

Answer 1

Actually it's 2 problems......

1)  t = ∆D/∆V = .125 km/20 km/hr = .00625 hr = 22.5 sec

2)  W = Σ(P*A) = 4*1.9E5*.022 = 16720 N

Answer 2

your are looking for time,  

distance is product of rate and time

d=rt

you know distance, you know rate , so solve for time.

the weight of the automobile is equal to the total pressure pushing down which is also the total pressure pushing up.

divide the pressure by the total area to find the total pressure and convert it to a weight unit.

I find it is much easier to learn formulas in sentence form rather than memorizing letter formulas.

Once you learn them that you you'll remember them for life.

Answer 3

sorry i can't help you with the second one, i haven't learned it yet, but i am very sorry that these two other guys are giving u the wrong answer for the first. they are both incredibly oversimplifying the question.

here's how i would solve it:

you need to use this formula for both cars to first solve (in terms of 't') the final distance where the cars will meet:

Xf = Xo + (Vo)(t) + 1/2(a)(t^2)

first i would convert km/hr to m/s:

50km/h = 13.89m/s

30km/h = 8.33m/s

i got these by first multiplying the km by 1000 to give meters, and then multiplying hours by 60 minutes and then by 60 seconds. so for example you would divide 50,000 by (60 x 60) to get 13.89m/s

so for car 1:

Xf = 0 + (13.89)(t) + (1/2)(0)(t^2) so all we have here is Xf = 13.89t, because acceleration is 0

for car 2:

Xf = 125 + (8.33)(t) + (1/2)(0)(t^2) so this becomes Xf = 125 + 8.33t

because again acceleration is 0. the '125' is in there because u need to set the inital displacement of car 2 relative to car 1, and the question says that it is 125m ahead of car 1.

ok so now we have two equations that equal the same Xf, so we can set them equal to each other:

125 + 8.33t = 13.89t

now its just a simple matter of solving for t:

13.89t - 8.33t = 125

5.56t = 125

t = 125 / 5.56

t= 22.5 seconds