Posted by **ruby** on Sunday, July 20, 2008 at 9:13pm.

earlier in this forum, marina asked the same question as i did. unfortunately, someone did answer, very clearly, but for some reason i remained to be a little lost. Here is the question:

A car traveling 90 km/h is 100 m behind a truck traveling 75 km/h. How

long will it take the car to reach the truck?

Can someone pleasee tell me the answer to this problem and HOW they solved it. THANK YOU!! =)

- physics -
**Ms. Sue**, Sunday, July 20, 2008 at 9:25pm
I don't know physics, but I can show you one way to solve this problem.

First, let's find how many meters each vehicle covers in one minute.

90 km/h = 90,000 m/h = 1500 m/minute

75 km/h = 75,000 m/h = 1250 m/minute

1500 - 1250 = 250 meters

100/250 = 0.4 minute

- physics -
**GK**, Sunday, July 20, 2008 at 9:36pm
Convert km/h to m/s:

(90 km/h)(1000m/1km)(1 h/3600s) = 25.000 m/s

(75 km/h)(1000m/1km)(1 h/3600s) = 20.833 m/s

Let time of catching up = t

The distance travelled by slower car = (20.833 m/s)(t)

The distance travelled by faster car = (25.000 m/s)(t)

The distance travelled by the faster car is 100 m longer than the slower car:

(20.833 m/s)(t)+100m = (25.000m/s)(t)

100 m = (25.000m/s - 20.833 m/s)t

Without units:

100 = (25.000 - 20.833)t

You should ba able to find the time in seconds, t, on your own.

- physics -
**drwls**, Monday, July 21, 2008 at 1:53am
The 100 m between the cars closes at a rate of 15km/h = 15,000 m/h

The gap becomes zero after 100/15,000 = 1/150 h = 0.40 min = 24 s

We all agree

- physics -
**ruby**, Monday, July 21, 2008 at 7:22pm
THANK YOU SOO MUCH!! THIS REALLY HELPED!!!

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