# physics

posted by .

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 -

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 -

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 -

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 -

THANK YOU SOO MUCH!! THIS REALLY HELPED!!!

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