Speed, Time and Distance


  1. Two trains of equal length take 10 seconds and 15 seconds respectively to cross a telegraph post. If the length of each train be 120 metres, in what time (in seconds) will they cross each other travelling in opposite direction ?









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    When a train crosses a telegraph post, it covers its own length.

    ∴  Speed of first train =
    120
    = 12 m/sec.
    10

    Speed of second train =
    120
    = 8 m/sec.
    15

    Relative speed = 12 + 8 = 20 m/sec.
    Required time =
    Total length of trains
    Relative Speed

    =
    2 × 120
    = 12 seconds.
    20

    Correct Option: C

    When a train crosses a telegraph post, it covers its own length.

    ∴  Speed of first train =
    120
    = 12 m/sec.
    10

    Speed of second train =
    120
    = 8 m/sec.
    15

    Relative speed = 12 + 8 = 20 m/sec.
    Required time =
    Total length of trains
    Relative Speed

    =
    2 × 120
    = 12 seconds.
    20


  1. Two trains of length 70 m and 80 m are running at speed of 68 km/hr and 40 km/hr respectively on parallel tracks in opposite directions. In how many seconds will they pass each other ?









  1. View Hint View Answer Discuss in Forum

    Relative speed
    = (68 + 40) kmph = 108 kmph

    =
    108 × 5
    m/s or 30 m/s
    18

    ∴  Required time =
    Sum of the lengths of both trains
    Relative Speed

    =
    70 + 80
    second = 5 seconds
    30

    Correct Option: C

    Relative speed
    = (68 + 40) kmph = 108 kmph

    =
    108 × 5
    m/s or 30 m/s
    18

    ∴  Required time =
    Sum of the lengths of both trains
    Relative Speed

    =
    70 + 80
    second = 5 seconds
    30



  1. Two towns A and B are 500 km. apart. A train starts at 8 AM from A towards B at a speed of 70 km/hr. At 10 AM, another train starts from B towards A at a speed of 110 km/hr. When will the two trains meet ?









  1. View Hint View Answer Discuss in Forum

    Let two trains meet after t hours when the train from town A leaves at 8 AM.
    ∴  Distance covered in t hours at 70 kmph + Distance covered in
    (t – 2) hours at 110 kmph = 500km
    ∴  70t + 110 (t – 2) = 500
    ⇒  70t + 110t – 220 = 500
    ⇒  180 t = 500 + 220 = 720

    ⇒  t =
    720
    = 4 hours
    180

    Hence, the trains will meet at 12 noon.

    Correct Option: B

    Let two trains meet after t hours when the train from town A leaves at 8 AM.
    ∴  Distance covered in t hours at 70 kmph + Distance covered in
    (t – 2) hours at 110 kmph = 500km
    ∴  70t + 110 (t – 2) = 500
    ⇒  70t + 110t – 220 = 500
    ⇒  180 t = 500 + 220 = 720

    ⇒  t =
    720
    = 4 hours
    180

    Hence, the trains will meet at 12 noon.


  1. A train travelling at 48 km/hr crosses another train, having half its length and travelling in opposite direction at 42 km/hr, in 12 seconds. It also passes a railway platform in 45 seconds. The length of the railway platform is









  1. View Hint View Answer Discuss in Forum

    Let the length of the train travelling at 48 kmph be x metres.
    Let the length of the platform be y metres.
    Relative speed of train
    = (48 + 42) kmph

    =
    90 × 5
    m./sec.
    18

    = 25 m./sec.
    and 48 kmph
    =
    48 × 5
    =
    40
    m./sec.
    183

    According to the question,
    x +
    1
    = 2
    25

    = 12
    ⇒ 
    3x
    = 12
    2 × 25

    ⇒  3x = 2 × 12 × 25 = 600
    ⇒  x = 200 m.
    Also, 
    200 + y
    = 45
    40/3

    ⇒  600 + 3y = 40 × 45
    ⇒  3y = 1800 – 600 = 1200
    ⇒  y =
    1200
    = 400 m.
    3

    Correct Option: D

    Let the length of the train travelling at 48 kmph be x metres.
    Let the length of the platform be y metres.
    Relative speed of train
    = (48 + 42) kmph

    =
    90 × 5
    m./sec.
    18

    = 25 m./sec.
    and 48 kmph
    =
    48 × 5
    =
    40
    m./sec.
    183

    According to the question,
    x +
    1
    = 2
    25

    = 12
    ⇒ 
    3x
    = 12
    2 × 25

    ⇒  3x = 2 × 12 × 25 = 600
    ⇒  x = 200 m.
    Also, 
    200 + y
    = 45
    40/3

    ⇒  600 + 3y = 40 × 45
    ⇒  3y = 1800 – 600 = 1200
    ⇒  y =
    1200
    = 400 m.
    3



  1. A train, 150m long, passes a pole in 15 seconds and another train of the same length travelling in the opposite direction in 12 seconds. The speed of the second train is









  1. View Hint View Answer Discuss in Forum

    Let the speed of the second train be x m/s

    Speed of first train =
    150
    = 10 m/sec
    15

    Relative speed of trains
    = (x + 10) m/s
    Total distance covered
    = 150 + 150 = 300 metre
    ∴  Time taken =
    300
    x + 10

    ⇒ 
    300
    = 12
    x + 10

    ⇒  12x + 120 = 300
    ⇒  12x = 300 – 120 = 180
    ⇒  x =
    180
    = 15 m/s
    12

    =
    15 × 18
    or 54 kmph.
    5

    Correct Option: D

    Let the speed of the second train be x m/s

    Speed of first train =
    150
    = 10 m/sec
    15

    Relative speed of trains
    = (x + 10) m/s
    Total distance covered
    = 150 + 150 = 300 metre
    ∴  Time taken =
    300
    x + 10

    ⇒ 
    300
    = 12
    x + 10

    ⇒  12x + 120 = 300
    ⇒  12x = 300 – 120 = 180
    ⇒  x =
    180
    = 15 m/s
    12

    =
    15 × 18
    or 54 kmph.
    5