physics

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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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