Q. A boat travels 50 km east, then 120 km north and finally it comes back to the starting point through the shortest distance. The total time of journey is 3 h. What is the average speed, in ${kmh}^{- 1},$ over the entire trip?
A) Zero
B) 100
C) 17
D) 33.33
Explanation
(b) $Time = \frac{distance}{average\ speed}$
$\Rightarrow Average\ speed$
$\ \ \ \ \ \ \ \ \ \ \ = \frac{distance}{time}$
$\ \ \ \ \ \ \ v = \frac{130 + 120 + 50}{3}$
$\ \ \ \ \ \ \ \ \ \ = \frac{300}{3} = 100\ {kmh}^{- 1}$
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Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.