# Motion problems #2

• Apr 9th 2010, 05:19 PM
Hellooo
Motion problems #2
Can someone please show me the steps needed to achieve the answers to this question?

Leonard need to get to Penny's house from his apartment- her house is just across a 4km wide river and is 3km upstream from Leonard's apartment with a current of 1km/h toward the east. Leonard can do one of two things: 1) he can swim on a path straight to Penny's house or 2) he can swim straight across the river and run the rest of the way on land. His swimming speed is 4km/h and his running speed is 6km/h. Which method will get Leonard to Penny's the fastest?

any help is much appreciated. =)
• Apr 9th 2010, 05:31 PM
mr fantastic
Quote:

Originally Posted by Hellooo
Can someone please show me the steps needed to achieve the answers to this question?

Leonard need to get to Penny's house from his apartment- her house is just across a 4km wide river and is 3km upstream from Leonard's apartment with a current of 1km/h toward the east. Leonard can do one of two things: 1) he can swim on a path straight to Penny's house or 2) he can swim straight across the river and run the rest of the way on land. His swimming speed is 4km/h and his running speed is 6km/h. Which method will get Leonard to Penny's the fastest?

any help is much appreciated. =)

What have you tried? Where are you stuck?
• Apr 9th 2010, 05:52 PM
Hellooo
I found the time it requires(1.2h, not totally sure if i'm correct) to travel directly across the river, but i'm not sure how to get the 2nd part.

I used the cosine law to find the velocity of Leonard swimming against the current( I got about 4.7km/h). After that i used the sine law to find the distance between Penny and Leonard which got 5.8km. I found the time by dividing the distance by velocity which appears to be 1.2h, which I'm not sure is correct.(Worried)
After that i found the time for 2nd method which turned out to be 1.7h which again I'm not sure if it's correct.(Angry)
• Apr 10th 2010, 06:28 AM
Hellooo
I'm not quite sure how to explain how i did it, but i a scanned picture of what i did.

http://i297.photobucket.com/albums/m...907/img012.jpg