The Speed of a moving body is the Distance travelled by it in unit Time.
Speed = Distance /Time
Distance travelled = Speed × Time
Total Time taken to cover some distance = Distance / Speed Speed is either measured in Kilometer/ hour or meter/
second
To convert Kilometer/ hour in meter/second,
If Distance=x km
Speed=x km/hr
Speed=x * 5/18 m/sec
If distance or speed in given=m/sec
Then speed=x* 18/5 km/hr
Concept -1
If a person covered two equal distance with different speed x & y kmph then
Average speed=(2xy)/(x+y)
Concept -2
If a person covered two different distance with two different
speed x & y km/hr respectively ,then average speed = [(a+b)xy] / (ay+bx)
a km distance is covered if x km/hr& b km distance is covered if y km/hr
Concept -3:
If a person walk (m/n)th of his natural speed then he takes T hr more, to reached office how much time he taken, when he walk with his natural speed= m/(m-n) T
Concept 4
Distance = (S1XS2) (T1-T2) /(S1-S2)
Example:
A man cover certain distance between his house and office with speed of 30 km/hr and late by 10 min. When he cover distance between house and office with speed of 40 km/hr then reach 5 min. early. Find the distance.
Solution
30 km/hr— 10 min late
40 km/hr—5min early
Distance=(30X40) (15/60)/(40-30) =30 km
Example :
A man leave Kavinager at 8:00 A.m. and reached Harinagar at 12:00 p.m. and other man from Harinagar at10:00 a.m. and reached kavinagar 2:00 p.m. when both are meet in the journey.
Solution :
Meeting time = 8.00 am + [(12.00 pm-8.00 am) (2.00pm-8.00am)/ [(12.00pm-8.00am) + (2.00pm-10.00am)8.00 A.M + 4 6/(4+6)=8.00 A.M+3 hr=11.00 am
Concept of Relative Speed:
Case1:
Two bodies are moving in opposite directions at speed V1 & V2 respectively. The relative speed is defined asVr =V1+V2.
Case2: Two bodies are moving in same directions at speed V1 & V2 respectively. The relative speed is defined asVr =|V1–V2|
1. If two trains (or bodies) start at the same time from points A and B towards each other and after crossing they take a and b sec in reaching B and A respectively, then:
(A's speed) : (B's speed) = (b : a)^1/2
EmoticonEmoticon