Bunuel wrote:
Two vehicles leave the same location at the same time. The first vehicle travels due east at 70 miles per hour. The other vehicle travels due west at 60 miles per hour. Assuming they continue at their respective speeds without stopping, how long (in hours) will it take for the two vehicles to be 455 miles apart?
(A) 2.75
(B) 3.5
(C) 4.25
(D) 4.75
(E) 5.5
The best method to answer this question will be using the
Relative speedRelative speed of the two objects is defined as change ijn distance between the two objects in unit timei.e. Relative speed of two moving objects with speed a and b
travelling in same direction = a-band Relative speed of two moving objects with speed a and b
travelling in Opposite direction = a+bThe the case given to us is the case of two trains moving in opposite directions hence
Relative Speed = 70+60 = 130 miles per hour
Time = Relative Distance / Relative Speedi.e. Time = 455 / 130 = 3.5 HoursAnswer: option B
ALTERNATIVE:Let, After t hours the distance between the two trains = 455 miles
Distance travelled by First train in t hours = Speed * Time = 70*t
Distance travelled by Second train in t hours = Speed * Time = 60*t
Total Distance travelled by the two trains together = 70t + 60t = 455 (Given)
i.e. 130t = 455
i.e. t = 3.5
Answer: option B
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