Motion in a Straight Line - Result Question 6
6. A bus travelling the first one third distance at a speed of $10 km / h$, the next one third at $20 km /$ $h$ and the last one-third at $60 km / h$. The average speed of the bus is
(a) $9 km / h$
(b) $16 km / h$
(c) $18 km / h$
(d) $48 km / h$
[1991]
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Answer:
Correct Answer: 6. (c)
Solution:
(c) Average speed $=\frac{s}{\frac{s / 3}{10}+\frac{s / 3}{20}+\frac{s / 3}{60}}$
$ =\frac{s}{s / 18}=18 km / h $
In case speed is continuously changing with time, then, $Vav=\frac{\int v d t}{\int d t}$
