A man walks on a straight road from his home to a market 2.5 km away with a speed of 5 km h ^{-1} .

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2.Motion in Straight Line

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A man walks on a straight road from his home to a market $2.5\; km$ away with a speed of $5 \;km h ^{-1} .$ Finding the market closed, he instantly turns and walks back home with a speed of $7.5 \;km h ^{-1} .$ What is the average speed of the man over the interval of time $0$ to $30\; min$ ?

A

$5$

B

$7.5$

C

$2.5$

D

$10$

Solution

Time taken to reach market $t_{1}=\frac{2.5}{5}=0.5$ hour $=30 min$

time taken to get back to home is $t_{2}=\frac {2.5}{7 .5}=.33$hour$=20 min$

Average velocity for $0-30$ in is $v=\frac{2.5}{5}=5 km / h$

Average speed for $0-30$ in is $s=\frac{2.5}{0.5}=5 km / h$

Standard 11

Physics

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