TIME,SPEED & DISTANCE – TSD
TSD- We all are very familiar with all three terms time, speed, and distance since our childhood but what is the application of all three terms from the exam perspective, we will see in this chapter.
Time - It had never been stopped and will
not be stopped until the earth exists so, we can easily say it is only increasing
function in this existing earth But in this chapter, we will see sometimes, we will make time constant
in the interval of two points which will very interesting so stay tuned till
last of this chapter.
Speed - Speed, we know it is in one hour/in unit time, how much you Travelled is called speed of that person. It is expressed generally in kilometers per hour. It has often been seen in examinations speed will be given either in m/s (meter per second) or in kilometers per hour. So how we will change from kilometer per hour to meters per second and vice-versa.
CONVERSION FROM KILOMETER PER HOUR TO METER PER SECOND-
Whenever you have to convert from km/hr to m/s, you need to multiply it by 5/18. Remember two numbers in your mind one is 5 and another is 18. Sometimes, while attempting competitive exams, we forgot which number will come in the numerator part and which no. will come in the denominator part. Look km/hr is a big unit than m/s .so when you need to convert from a bigger unit to a smaller one just keep a smaller no. (5) in the numerator part while the other (18) in a denominator part so, finally we multiply the bigger unit (km/hr) with 5/18 to get the smaller unit (m/s). We can do just reversed while converting smaller unit(m/s) to bigger unit (km/hr) by keeping the bigger number(18) in the numerator part and a smaller number(5) in the denominator part so, finally we multiply m/s with 18/5 to get speed in km/hr. We can best understand this with the figure below.
Example1. If the speed of a person is 36 km/hr. What will be his speed in m/s?
Sol- Just multiply with 5/18.
36 × 5/18 = 10 m/s.
Example 2. Convert 10 m/s , 40 m/s and 60 m/s into Km/hr.
Sol- 10 m/s = 10 × 18/5 = 36 km/hr
40 m/s= 40 × 18/5 = 144 km/hr
60 m/s = 60 × 18/5 = 216 km/hr
DISTANCE - It is nothing but the whole path travelled without making any shortcut /displacement. Normally we measure distance in their SI Unit meter.
The short distance we measure in meters.
Long-distance we measure in kilometer.
The very short distance we measure in cm generally
Conversion chart – We can easily understand through the given figure, it will help you to solve questions quickly in your exam time.
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Relation among three terms -
DISTANCE = SPEED × TIME
Based on it, we can find the remaining two which is shown below -
SPEED = DIS/ TIME
----------------------------------------------1
TIME = DIS /SPEED
---------------------------------------------2
We will only keep one relation in mind which is “dis = speed × time ".
if anything apart from distance is being asked then just keep distance in
numerator part and rest of what we left will keep
in the denominator part, you can
easily see in equations 1 and 2.
SOME IMPORTANT KEY CONCEPTS – CASE 1- WHEN DISTANCE = Fixed Value /Constant
1. WHAT WILL HAPPEN WHEN IN BETWEEN TWO POINTS /TWO PLACES - WHENEVER IF IN A QUESTIONS, IT HAS BEEN GIVEN THAT IN BETWEEN TWO POINTS OR IN BETWEEN TWO PLACES THEN ALWAYS KEEP IN MIND THAT THERE IS CONSTANT /FIXED DISTANCE BETWEEN TWO POINTS. WHENEVER DISTANCE IS FIXED THEN
IF DISTANCE = FIXED BETWEEN TWO PLACES/POINTS THEN
I.
SPEED = 1/TIME
II.
TIME = 1/SPEED
III. SPEED IS INVERSELY
PROPORTIONAL TO TIME.
IV.
IN TERMS OF RATIO - IF
RATIO OF SPEED IN GIVEN TWO POINTS (SUPPOSE FROM PATNA TO DELHI) IT IS A: B THEN RATIO OF THE TIME WILL BE B: A.
V.
IN TERMS OF RATIO – IF RATIO OF TIME IS GIVEN IN FIXED INTERVAL
/DISTANCE C: D THEN RATIO OF SPEED WILL
BE D: C.
CASE2 - WHEN SPEED IS FIXED IN THE WHOLE JOURNEY /PATH.
DIS= SPEED × TIME
DIS = CONSTANT ×TIME
I.e. Distance is directly proportional to the time
means, if distance increase then time will increase and vice versa.
Ø If distance ratio is given in a question a: b
then the same ratio will be for time because both are proportional to each - other.
Distance - a: b
Time - a : b
Ø If time ratio is given in the above context suppose it is a: b then, speed ratio will be also a: b .
Time ratio - a: b
Speed ratio - a
: b
CASE 3 - WHEN TIME IS KEPT CONSTANT / IN EQUAL INTERVAL FOR JOURNEY –
DIS
= SPEED × TIME
DIS =
SPEED × CONSTANT (VALUE)
SO, DISTANCE IS DIRECTLY PROPORTIONAL
TO SPEED.
Ø IF SPEED RATIO IS
GIVEN a: b then, distance ratio will be
also a: b.
Speed - a: b
Distance - a: b
Ø Similarly, if the distance ratio is given a: b then
, speed ratio will be also a: b
AVERAGE SPEED - IT IS THE RATIO OF TOTAL DISTANCE COVERED IN TOTAL TIME.
AVG SPEED = TOTAL DISTANCE IN JOURNEY / TOTAL TIME TAKEN
DURING THE JOURNEY.
APPLICATION OF ALL ABOVE CONCEPTS WITH PROBLEMS
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TYPE 1 – WHEN DISTANCE IS FIXED
Q1. An airplane covers a certain distance at a speed of 240 km/hr in 5 hour, To cover the same distance in 5/3 hours it must travel at a speed of
a. 300 km/hr
b. 360 km/hr
c c. 600 km/hr
d. d. 720 km/hr
Sol- Here , easily we can find distance by
reading first line statement of questions in each hour 240 km travels so , in 5
hour = 240 × 5 = 1200 km
So ,
distance = 1200 which is fixed in
another trip from the questions
Time = 5/3 hours
So
, speed = 1200 / (5/3) =
1200 ×3/5 = 720 km/hr
Here
distance is fixed in journey = 240 × 5 = 1200 km
Time
- 5 :
5/3
Or, 15 : 5
or, 3: 1
Since 1 unit/part = 240 km/hr so , 3 unit/part = 3 ×240 = 720 kmphr
Note – Try to use second method that will save your valuable time in exam and less stress.
Q2. Walking at ¾ of his usual speed, a man is 3/2 hours late. His usual time to cover the same distance in hours is?
a. 9/2 hours
b. 11/2 hours
c. 4 hours
d. 5 hours
Sol-
Here , again distance in a given interval is fixed so go through ratio method to solve easily
Here
, time difference in terms of ratio =
4-3 = 1 unit /part
And in questions it
is equal to = 3/2 hours
So , 1 unit =
3/2 hours
So, 4
unit = 3 × 3/2 = 9/2 =
4.5 hours
Note - Always
take denominator value here it is 4 part as usual speed part according to sentence so, numerator part
will become normal speed part which is
3 part. This approach will give you
less time and faster solution which is most important in competitive exams.
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