TIME,SPEED AND DISTANCE
Tricks 1: ST=D (remember it as STD calling)
Speed × Time = Distance
From STD method, you can easily derive all the formulas.
Speed = Distance ÷ Time
Time = Distance ÷ Speed
Tricks 2: Speed is inversely proportional to time.
Please understand that, If speed is high then time taken to cover x distance will be less and if speed is slow then time taken to cover the same distance x, will be more.
Speed ∝ (1 / Time)
-distance covered is constant
Tricks 3: To convert km/hr to m/sec and m/sec to km/hr.
We know, km/hr is bigger value and m/sec is smaller so what we do to convert bigger value into smaller?
We divide by a value which has greater denominator than numerator. so to convert km/hr into m/sec we multiply by 5÷18, where 18 (denominator) is greater than 5 (numerator).
x km/hr = x × 5÷18 m/sec
Similarly, To convert m/sec to km/hr, we do the reverse process.
x m/sec = x*(18/5) km/hr
Tricks 4: Average Speed
If a person or object covers a certain distance atkmph and an equal distance at kmph, the average speed of the whole journey.
Average speed = 2xy ÷ (x + y)
Tricks 5: Ration of speed
If the ratio of the speed of A and B is,then the ratio of the time taken by them to cover the same distance is or b:a
Tricks 6: Relative Speed
If two objects are moving in the same direction atm/s and m/s respectively where then their relative speed m/s.
a man, travelling in train can count 21 poles in one minute.If they are known to be 50 meters apart. What is the speed train travelling?
Step 1:Find out all the values given in the question and note down.
In this example, we need to find out all the values given in the question.
Number of poles = 21
Distance b/w each pole = 50 meter.
Step 2: Draw a basic sketch of distance and write values on that.
Draw a sketch, in this example drwaing a sketching don’t benefit much.
Pole 1 |—|—|—|—|—|—|—|—|—|—|—|—|—|—|—|—|—|—|—|—|—|—|—| Pole 21
Step 3: Covert all the values in single unit (either km/h or m/sec)
Distance b/w two pole is 50 meter, convert it to km/h ⇒ 50/1000 ⇒ 1/20
Time taken is 1 minute ⇒ 1/60 hr
Step 4: Try to find all the possible values from given values.
Total Distance: 21 × 1/20 ⇒ 21/20
Step 5: Put all the finding in equation and get the desired answer.
Formula, from tricks 1, ST = D
S (1/60) = 21/20
s= 63 km/hr — Answer