Speed tells us how fast or slow an object is moving. It is directly proportional to distance and inversely proportional to time which means if speed is high then distance covered is more and time taken will be less.
Speed =
Distance
Time
Distance = Speed x Time
Time =
Distance
Speed
Unit of speed is km/hr or m/sec. In the question, you might be given speed in km/hr, and you need to convert it into m/sec. For this use the below formula-
x km/hr = x *
5
18
m/sec
Eg- Speed of a car is 36 km/hr. What is the speed of the car in m/sec? Ans is 36 x
5
18
= 10 m/sec
To Convert from m/sec to km/hr, use this formula-
x m/sec = x *
18
5
km/hr
Eg- Speed of a car is 10 m/sec. What is the speed of the car in km/hr? Ans is 10 x
18
5
= 36 km/hr
If the ratio of speed between X and Y is x : y then the ratio of time taken to cover a particular distance will be
1
a
:
1
b
Suppose a person covers a certain distance at x km/hr and an equal distance at y km/hr. Then, the average speed for the whole journey is
2xy
x + y
.
We can extend this formula for n equal distances. Let say a person covers a certain distance at s1 km/hr, and another equal distance at s2 km/hr, another equal distance at s3 km/hr and so on. In that case, average speed for the whole journey is