(adsbygoogle = window.adsbygoogle || []).push({}); 1. The problem statement, all variables and given/known data

Two boats start together and race across a 42 km wide lake and back. Boat A goes across at 42 km/h and returns at 42 km/h. Boat B goes across at 21 km/h, and its crew, realizing how far behind it is getting, returns at 63 km/h. Turnaround times are negligible, and the boat that completes the round-trip first wins.

Which boat wins and by how much(km)?

2. Relevant equations

Conversions

Average Speed = Total distance/total time

3. The attempt at a solution

I took 42km/h * 1h/84km = 1/2h for boat A to travel there and 1/2 h to travel back.

21km/h * 1h/84km = 1/4h for boat B to travel there leaving it 3/4h to travel back.

Next I took the speed and multiplied by the hours:

42km/h * 1/4h = 10.5 km

21km/h * 1/4h = 5.25 km

63km/h * 3/4h = 47.25 km

Then added the distance of boat B and subtracted boat A:

(47.25km + 5.25km) - (10.5km + 10.5km) = 31.5km

What am I doing wrong??

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# Homework Help: 1D Kinematics : Speed & Distance

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