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Time and Distance

Speed:
Speed is the average rate at which distance is covered by a moving body
‘s’ = distance(d)/time taken(t) or s = d/t

if Speed is constant then d αt
if Distance is constant then sα1/t
if time is constant then dα s

Average speed:
If certain distance is covered in parts at different speeds,then
Average Speed=t1

Conversions :
1 km/hr = 5/18 m/sec
1 m/sec = 18/5 km/hr

Relative speed:
(1) If two objects(Train) are moving in the same direction , then relative
speed of one with respect to other is the difference of the speeds.

(2) If two objects(Train) are moving in the opposite direction , then
relative speed of one with respect to other is the sum of the
speeds.
Time taken by the train in passing a pole or standing man= t2

Time taken by the train to cross the bridge= t3

For Example-A train covers a distance in 50 min, if it runs at a speed of 48kmph on an average. The speed at which the train must run to reduce the time of journey to 40min will be.
Explanation :
Time
         =50/60hr
          =5/6hr
Speed = 48mph
distance =S×T
         =48×(5/6)
          =40 km
Time
         =40/60hr
          =2/3 hr

New speed
         =48×(2/3)kmph
          =32 kmph