Page 126 - ICSE Math 6

Conversion of units of speed
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• To convert km h into m s –1
1 km = 1,000 m and 1 h = 60 × 60 s = 3,600 s Try These
1000 m 5 1. By what number will you
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\ 1 km h = = m s –1
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3600 s 18 multiply a speed in km s
5
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to get the speed in m min ?
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Thus, to convert km h into m s , multiply by 18 . 2. If distance = 2 km and time
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• To convert km h into cm s . = 6 min, find speed in m s .
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1 km = 1,000 m = 1,000 × 100 cm = 1,00,000 cm and 1 h = 60 × 60 s = 3,600 s
100000 cm 250
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\ 1 km h = = cm s –1
3600 s 9
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Thus, to convert km h into cm s , multiply by 250 .
9
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• To convert m s into km h .
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As 5 m s = 1 km h –1
18
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\ 1 m s = 1 km h = 18 km h –1
5/18 5
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Thus, to convert m s into km h , multiply by 18 .
5
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• To convert cm s into km h .
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As 250 cm s = 1 km h –1
9
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\ 1 cm s = 1 km h = 9 km h –1
250/9 250
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Thus, to convert cm s into km h , multiply by 9 .
250
Example 7: Convert the following.
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(a) 90 km h into m s (b) 20 m s into km h –1
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(c) 70 cm s into km h (d) 63 km h into cm s –1
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Solution: (a) 90 km h = 90 × 5 m s = 25 m s (multiply by 5 )
18 18
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(b) 20 m s = 20 × 18 km h = 72 km h (multiply by 18 )
5 5
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(c) 70 cm s = 70 × 9 km h = 2.52 km h (multiply by 9 )
250 250
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(d) 63 km h = 63 × 250 cm s = 1,750 cm s (multiply by 250 )
9 9
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Example 8: An aeroplane covers 1,500 km in 2 hours. Find its speed in:
2
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(a) m s (b) km min –1
1 5
Solution: (a) Time = 2 hours = hours
2 2
Distance 1500 km 1500 × 2
Speed = = = km h –1
Time 5/2 h 5
= 600 km h –1
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