Two boats start together and race across a 60-km-wide lake and back. B



Answered question


Two boats start together and race across a 60-km-wide lake and back. Boat A goes across at 60 km/h and returns at 60 km/h. Boat B goes across at 30 km/h, and its crew, realizing how far behind it is getting, returns at 90 km/h. Turnaround times are negligible, and the boat that completes the round trip first wins. What is the average velocity of the winning boat?

Answer & Explanation

Nadine Salcido

Nadine Salcido

Beginner2022-01-06Added 34 answers

Step 1
Here width of the lake
Up speed of the boat-1 v1U=60km h1
Down speed of the boat-1 v1D=60km h1
Up speed of the boat-2 v2U=30km h1
Down speed of the boat-2 v2D=90km h1
The time taken by the boat-1 for the trip is
1) =60km60km h1+60km60km h1
And the time taken by the boat-2 for the trip is
2) =60km30km h1+60km90km h1
Because from equations (1) and (2), we can see that
Therefore boat-1 wins the trip by 0.7 h
Because the winning boat-1 returns at the same point from where it stars. Therefore its displacement is zero. So the average velocity of the winning boat-1 is
v=displacementtime taken
=0m s1


Beginner2022-01-07Added 33 answers

Step 1
Average speed for boat A equals:
(and because boat A has constant speed during all trip)


Expert2022-01-10Added 613 answers

Step 1
Average Velocity=Total displacementtime taken
Time taken=2hr
Total displacement=0km,
Since boat A starts at starting point of lake and returns back after completing race at the same starting point, So total displacement is zero.
So, Average velocity=0km2hr=0kmhr

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