November 17th, 2007, 10:25 AM  #1 
Newbie Joined: Nov 2007 From: UK Posts: 5 Thanks: 0  Relative Motion Question
Hi guys, been givin this question for a tutorial and tis really annoying me, not sure what it states. would be brill to get some help... V=velocity Three cars travelling with constand V along a straight road. car A is travelling in same direction as B but 10 mph faster whilst C is travelling in opposite direction with speed of 100mph relative to A. What is the V of C relative to B? (90?) What is the V of B relative to C? (90?) 
November 17th, 2007, 07:49 PM  #2 
Senior Member Joined: Oct 2007 From: Chicago Posts: 1,701 Thanks: 3 
You are correct: A is going 10 mph faster than B, so B is going 10 mph in the other direction (with respect to A). Since C is going 100 mph in the other direction (with respect to A), C is going 100  10 = 90 mph. I would use the positive number +90 with a qualifier of some sort in both cases; If you follow the reference frame, C with respect to B should be 90, but if you follow the statement that "C ... speed of 100 miles relative to A", than C with respect to B should be +90. Bloody physicists are always so imprecise with their use of language. 
November 18th, 2007, 01:27 AM  #3 
Newbie Joined: Nov 2007 From: UK Posts: 5 Thanks: 0 
Ok but the question states A is travelling in the same direction as B.


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