# Physics 100 homework help

1. Sep 6, 2007

### alda00

I have a homework problem that I cant solve, I have been spending some time on it. It goes like this...

An automobile traveling 95km/ overtakes a 1.10 km long train traveling i the same direction on a track parallel to the road. If the train's speed is 75kh/h how long does it take for the car to pass it, and how far will the care have traveled in this time?

2. Sep 6, 2007

### rootX

you must show your work, first.

try considering this question:
An automobile travelling 95 km/hr is 1.10 km behind a train(a point source) that is travelling at 75 km/hr, and so how long does it takes...?

3. Sep 6, 2007

### mjsd

always draw a diagram if in doubt

4. Sep 6, 2007

### B-80

remember that all motion is relative so think of the way the car is moving relative to the train, so how long would it take?

5. Sep 7, 2007

### mjsd

by the way, with that sort of speed, I don't think it is a question involving special relativity either, so standard newtonian mechanics and Galilean relativity are applicable

6. Sep 8, 2007

### cks

Denote the position of the front part of the train as y

y=75t+1.10

Denote the position of the car as

x=95t

You can see the logic of the equations above, at time t = 0, y=1.10km (correct!)
At time t=0, x=0(correct)

with the derived equations of the positions of the train and car, and for the car to overtake the train, their position have to be the same at a certain time t, so, what should you do???