Problem 4.18 - Enhanced - with Feedback Part A How fast is the river flowing? Ex

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Problem 4.18 - Enhanced - with Feedback

Part A

How fast is the river flowing?

Express your answer with the appropriate units.

km/h

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PHYS 201 SPRING 2017

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Assignment 6

Problem 4.18 - Enhanced - with Feedback

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Problem 4.18 - Enhanced - with Feedback

A boat takes 2.70 hours to travel 35.0 km down a river, then 6.50 hours to return.

You may want to review ( pages 91 - 92) .

Part A

How fast is the river flowing?

Express your answer with the appropriate units.

km/h

SubmitMy AnswersGive Up

Provide FeedbackContinue

Explanation / Answer

A)
let the velocity of boat be u m/s and velocity of river be v km/h

relative speed of of boat respect to ground while travelling down = (u+v) km/h
relative speed of of boat respect to ground while travelling upward = (u-v) km/h
distance = 35.0 km

then we 2 equation,
35/(u+v) = 2.70
35/(u-v) = 6.50

so it becomes,
u+v = 12.96
u-v = 5.38

we need to find v. So subtract both equations above,
u+v - (u-v) = 12.96- 5.38
2v = 7.58
v = 3.79 km/h

Answer: 3.79 km/h

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