Introduction : Time, speed and distance

1 km/hr to m/sec conversion:

2. relative speed of a moving body with the speed x km/h in relation to the other moving body with speed of y km/h:
(a)in same direction is the difference of their speed (x-y) km/h.
(b) in opposite direction  is the sum of their speed (x+y) km/h.

3. if two trains of length x km and y  km are moving in opposite direction at u km/h and v km/h Then time taken by trains to cross eachother = {x+y/u+v} h

4. if two trains of length x km and y km are moving in the same direction at u km/h
And v km/h  , where u>v , then time taken by faster train to cross the slower train
= {x+y/u-v} h.

5. speed of the boat in still water =  [ u+v/2] km/h.

6. speed of the stream = [ u-v/2] km/h.

7. in travelling equal distance with speeds x and y , the average speed is expressed a = {2xy/x+y}

Downstream speed u km/h
Upstream speed v km/h

SAMPLE PROBLEMS :

1. A train can travel 50% faster than a car. Both start from point A at the same time and reach point B 75 kms away from A at the same time. On the way, however, the train lost about 12.5 minutes while stopping at the stations. The speed of the car is:

a. 100 kmph
b. 110 kmph
c. 120 kmph
d. 130 kmph

2. An aeroplane covers a certain distance at a speed of 240 kmph in 5 hours. To cover the same distance in 1 2/3  hours, it must travel at a speed of:

a. 300 kmph
b. 360 kmph
c. 600 kmph
d. 720 kmph

3. A man is walking at a speed of 9 km/h. After every km he takes rest for 9 min. how much time will he take to cover a distance of 27 km?

a. 6 h
b. 6 h 45 min
c. 6 h 54 min
d. 6 h 35 min

4. A boat takes 90 minutes less to travel 36 miles downstream than to travel the same distance upstream. If the speed of the boat in still water is 10 mph, the speed of the stream is:

a. 2mph
b. 2.5mph
c. 3mph
d. 4mph

5. A car travelling with 5/7 of its actual speed covers 42 km in 1 hr 40 min 48 sec. Find the actual speed of the car.

a. 17 6/7 km
b. 25 km/ hr
c. 30 km/ hr
d. 35 km/ hr

6. A train passes a station platform in 36 seconds and a man standing on the platform in 20 seconds. If the speed of the train is 54 km/hr, what is the length of the platform?

a. 120m
b. 240 m
c. 300 m
d. None of this