Simple relative velocity question?

Question

It's simple enough, but I'm having a brain fart. I have the answer, but I need to know how to get there. Thanks.

Question: How long does it take an automobile traveling in the left lane of a highway at 60.0 km/h to overtake (become even with) another car that is traveling in the right lane at 40.0 km/h when the cars' front bumpers are initially 100 m apart?

Answer: 18.0 s

Answer 1

You can imagine the slower car (car A) to be not moving, and the other (car B) to be travelling at a speed of 60 - 40 = 20 km/h.

Now the problem is simplified to "how much time does it take for the car travelling at 20 Km/h (car B*) to cover 100m?"

It fairly simple: I know you can do it yourself, but here's the details:

convert km/h to m/s, the conversion factor is 0.277777, so:

20 km/h = 5.5555 m/s

so the car B* is travelling at 5.5555 metres per second.

t = 100 m / 5.555 m/s = 18.00 s

it comes out prcisely 18.00 if you consider that it's 5.5 with a periodic 5.

Answer 2

No. the fee of light in a vacuum is an absolute. bear in ideas that velocity is a function of area (distance) and time. Einstein got here across that the two time and area are relative, yet that lightspeed can't exchange. If 2 photons (or 2 anythings) shuttle in opposite instructions on the fee of light, they're going to disappear over one yet another's adventure horizon. meaning that from the attitude of each and every, the different has disappeared from the observable universe.

Answer 3

The difference in speed is 20 kph so the time to travel 100 m (or 0.1 km) is:

(0.1 km / 20 km/h) * 3600 sec/hr = 18 sec