Go Back   Physics Help Forum > Lobby > New Users

New Users New to PHF? Post up here and introduce yourself!

Reply
 
LinkBack Thread Tools Display Modes
Old Jul 25th 2018, 11:57 AM   #1
Junior Member
 
Join Date: Jul 2018
Posts: 16
ships in the night

Hi folks,

The velocity of ship A relative to ship B is 10.0 km/h in a direction North 45 East. If the velocity of B is 20 km/h in a direction N 60 W, find the actual velocity of A in magnitude and direction.

The attachment shows my sketch.
Vector A relative to B (OA in the sketch) is $\underline{a} - \underline{b}$

Vector A is AB
Vector B is OB

so A relative to B = AB + BO or AB - OB

to calculate vector A I used the cosine rule

magnitude of $AB^2 = \underline{a^2} = 10^2 + 20^2 -2.10.20 \cos 105 $

$\underline{a}^2 = 603.53$

$\underline{a}= 24.6$

this is the wrong answer. Correct is 19.8

can't see where I am going wrong!
Attached Thumbnails
ships in the night-scan-60.jpeg  

Last edited by uxinox; Jul 25th 2018 at 12:01 PM.
uxinox is offline   Reply With Quote
Old Jul 26th 2018, 03:49 AM   #2
Junior Member
 
Join Date: Jul 2018
Posts: 16
It's OK guys. Just needed to sleep on it. Problem solved.
uxinox is offline   Reply With Quote
Reply

  Physics Help Forum > Lobby > New Users

Tags
night, ships



Thread Tools
Display Modes


Similar Physics Forum Discussions
Thread Thread Starter Forum Replies Last Post
Solar Energy Conversion at Night SophiaL Thermodynamics and Fluid Mechanics 3 Feb 20th 2017 01:54 PM
Why the house is hot at night ahmadbakri Thermodynamics and Fluid Mechanics 1 Feb 27th 2009 09:17 AM


Facebook Twitter Google+ RSS Feed