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March 28, 2017

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can you show me how to do this mathematically

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?

  • physics - ,

    Try this.
    car|--0.100 km--|-------d---------|
    t r u c k xxxxxx|-------d---------|
    The truck travels a distance, d km, while the car travels d + 0.100 km.
    distance = rate x time. The time must be equal so
    time = distance/rate
    time for truck = d/75
    time for car = (d+0.100)/90
    time = time
    d/75 = (d+0.100)/90
    solve for d and I get 0.5 km. So the truck travels 0.5 km and the car travels 0.6 km. How long does that take.
    d = r*t
    t = d/r
    t = 0.5/75 = 0.00667 hr or
    t = 0.6/90 = 0.00667 hr.
    You can convert 0.00667 hr to minutes, then to sec by
    0.00667 hr x (60 min/hr) x (60 sec/min) = I get 24 seconds but check my work.

  • physics - ,

    There is another way to do this which is a little shorter.
    Note that the difference between 90 km/hr and 75 km/hr is 15 km/hr. So we ask ourselves how long it takes to cover that additional 0.1 km at the rate of 15 km/hr. That is t=d/r = 0.100/15 = 0.00667 hr. Voila!

  • physics - ,

    Thank You

  • physics - ,

    24 seconds

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