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Why did we assume it to be 45 degrees?

by madinsane
Tags: assume, degrees
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madinsane
#1
Mar9-12, 08:57 AM
P: 32
1. The problem statement, all variables and given/known data
a motorist drives south at 20 m/s for 3 min, then turns west and travels west at 25m/s for 2 min, and finally travels n/w at 30 m/s for 1 min. for this 6 minute trip, find the net vector displacement


2. Relevant equations



3. The attempt at a solution

distance 1: 20m/s * 3min * 60s/min = 3600m south
distance 2: 25m/s * 2.6min * 60s/min = 3900m west
distance 3: 30m/s * 1min * 60s/min * cos45 = 1273m west
................ 30m/s * 1min * 60s/min * sin45 = 1273m north

My real problem is why we assumed the angle is 45 degrees? Why did we dissect the 90 degree angle in half for the north west if it doesnt tell us in the problem?
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Doc Al
#2
Mar9-12, 09:12 AM
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Quote Quote by madinsane View Post
My real problem is why we assumed the angle is 45 degrees? Why did we dissect the 90 degree angle in half for the north west if it doesnt tell us in the problem?
It says that it travels n/w = northwest, which means half-way between North and West. That's where the 45 degrees comes in.
madinsane
#3
Mar9-12, 09:19 AM
P: 32
Quote Quote by doc al View Post
it says that it travels n/w = northwest, which means half-way between north and west. That's where the 45 degrees comes in.
thank you!

skeptic2
#4
Mar9-12, 09:28 AM
P: 1,813
Why did we assume it to be 45 degrees?

In the problem statement it says "travels west at 25m/s for 2 min" yet in your attempt at a solution you change it to 2.6 min. Why?
madinsane
#5
Mar9-12, 10:53 AM
P: 32
Quote Quote by skeptic2 View Post
In the problem statement it says "travels west at 25m/s for 2 min" yet in your attempt at a solution you change it to 2.6 min. Why?
just a silly typo sorry


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