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March 30, 2017

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An automobile traveling 95 overtakes a 1.10--long train traveling in the same direction on a track parallel to the road.

Q1: If the train's speed is 75 , how long does it take the car to pass it

Q2:How far will the car have traveled in this time?

Q3:What is the time if the car and train are traveling in opposite directions?

Q4:How far will the car have traveled if the car and train are traveling in opposite directions

  • physics - ,

    It is easier to solve this problem if we introduce the relative velocity of the car (relative to the train). The velocity of the car relative to the train is (95-75) km/h=20 km/h.

    In the relative description the train is not moving and the car is moving with constant speed 20 km/h.
    a. The time the car needs to pass the train is
    t = length of the train/relative speed = 1.1 km/20 (km/h) = 0.055 h =198 s.
    b. To find the actual traveled distance of the car we just need to multiply the traveled time (0.055 h) by the actual speed of the car:
    L = 95•0.055 = 5.225 km
    c. The relative speed is v1= 95+75 =170 km/h
    The time the car needs to pass the train in this case is
    t1= length of the train/relative speed v1= 1.1 km/170 (km/h)=
    = 0.00647h =23.3 s.
    d. To find the actual traveled distance of the car we just need to multiply the traveled time (0.00647 h) by the actual speed of the car:
    L = 95•0.00647 = 0.615 km.

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