Here we will learn the conversion of units of speed

(i) Conversion of km/hr into m/sec

(ii) Conversion of m/sec to km/hr

How to convert km/hr into m/sec?

km/hr = 1 km/1 hr = 1 × 1000 m/60 × 60 sec = 1000/3600 m/sec = 5/18 m/sec

So, we say that to convert km/hr into m/sec, we multiply by 5/18.

**Solved examples on conversion of km/hr into m/sec: **

**1.** Convert 72 km/hr to m/sec

**Solution:**

72 km/hr

= 72 × 5/18 m/sec

= 20 m/sec

**2.** The speed of
the bicycle is 90 km/hr, what is its speed in m/sec?

**Solution: **

Speed of bicycle = 90 km/hr

To convert the speed into m/sec, we multiply by 5/18

Therefore, speed of bicycle = 90 × 5/18 m/sec = 25 m/sec

**3.** A car covers a
distance of 100 km in first two hours, 120 km in next 1 hour and 32 km in next
1/2 hour. Convert the speed into m/sec.

**Solution: **

Total distance covered by the car = (100 + 120 + 32) km = 252km

Total time taken = (2 + 1 + 1/2) hr = (4 + 2 + 1)/2 = 7/2 hr

Therefore, average speed = Distance covered/Time taken

= 252 km/(7/2) hr

= 252/1 × 2/7 km/hr

= 72 km/hr

To convert the speed into m/sec, we multiply by 5/18

Therefore, 72 km/hr = 72 × 5/18 = 20 m/sec

How to convert m/sec to km/hr?

m/sec = 1m/1sec = (1/1000) km/(1/60 × 60) hr = 60 × 60 /1000 km/hr = 18/5 km/hr

So, we say that to convert m/sec into km/hr, we multiply by 18/5

**Solved examples on conversion of
km/hr into m/sec:**

**1.** Convert 40 m/sec to km/hr

**Solution: **

40m/sec

= 40 × 18/5

= 144 km/hr

**2.** The speed of a
cyclist is 4 m/sec. find the speed in km/hr.

**Solution: **

Speed of a cyclist = 4 m/sec

To convert the speed in km/hr, we multiply by 18/5

Therefore, speed of the cyclist = 4 × 18/5 km/hr

= 72/5 km/hr

= 14.4 km/hr

Hence, we have learnt the conversion of units of speed from km/hr to m/sec and m/sec to km/hr.

Relationship between Speed, Distance and Time

Problems on Calculating Distance

Two Objects Move in Same Direction

Two Objects Move in Opposite Direction

Train Passes a Moving Object in the Same Direction

Train Passes a Moving Object in the Opposite Direction

Two Trains Passes in the Same Direction

Two Trains Passes in the Opposite Direction

**8th Grade Math Practice**

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