Question:
An athlete takes 30 second to complete a race of 450 meter. Find the speed of the athlete in kilometre per hour.
Correct Answer
54 kilometer/hour
Solution And Explanation
[Strategy to solve the Question: (1) Calculate the speed in m/s and then change this speed into kilometre per hour. (2) change the distance into km and time into hour and then calculate the speed using these units. This speed will be in the required kilometer per hour]
Given,
Distance = 450 meter
Time = 30 second
Now we know that,
Speed = Distance/Time
Thus, speed of the given athlete
= 450 meter /30 second
= 15 meter per second
⇒ Speed = 15 m/s
Conversion of speed from m/s to km/h
To convert meter per second (m/s) to kilometre per hour (km/h) we need to multiply m/s by 18 /5 .
Thus, 15 m/s
= 15 3 × 18 / 5 km/h
= 3 × 18 = 54 km/h
Thus, speed of the given athlete = 54 km/h Answer
Second method to calculate the speed in km/h using distance given in meter and time given in second.
Here, given distance = 450 meter
= 450 /1000 km
[∵ 1000 meter = 1 km. Thus, 1 meter = 1 /1000 km]
= 45 /100 km
Thus, distance = 0.45 km
And, given time = 30 second
= 30 /60 × 60 hour
= 30/3600 120 hour
= 1/120 hour
Thus, time = 1/120 hour
Calculation of speed in km/h using formula
Now we know that,
Speed = Distance/Time
Thus, the speed of the given athlete in km/h
= 0.45 km /1/120 hour
= 0.45 km × 120/1 hour
= 0.45 × 120 km/h
= 54 kilometer per hour
Thus, speed of the given athlete = 54 km/h Answer
[After observing the result obtained here, it is better to calculate the speed in m/s using the given units and after that change the speed from m/s to the required km/h.
The using of type of method depends upon the situation. ]
Calculation of speed using Unitary Method when time and distance are given]
Given, Distance = 450 meter
And, Time = 30 second
∵ In 30 second, the distance covered = 450 m
∴ In 1 second, the distance covered = 450 m /30 second
= 15 m/s or 15 meter per second
Conversion from m/s to km/h
Here, speed = 15 m/s
This means, speed = 15 m/1 s
= 15/1000 km/1/60 × 60 hour
= 15/1000 km/1/3600 hour
= 15/1000 km × 3600/1 hour
= 15 × 36/10 km/h
= 540/10 km/h
⇒ Speed in km/h = 54 km/h
Thus, speed of the given athlete = 54 km/h Answer
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(2) Find the distance covered by a car in 20 hours if it covers a distance of 100 km in 10 hours.
(3) At a certain speed a cyclist covers a distance of 88 km in 3 hours. How much distance will it cover in 4 hour?
(4) Find the distance covered by a motor bike in 23 hours if it covers a distance of 90 km in 13 hours.
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(6) At a certain speed a car covers a distance of 4 km in 2 hours. How much distance will it cover in 3 hour?
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