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VCE Stuff => VCE Science => VCE Mathematics/Science/Technology => VCE Subjects + Help => VCE Physics => Topic started by: kenhung123 on January 18, 2010, 11:16:31 pm

Title: Kinda weird
Post by: kenhung123 on January 18, 2010, 11:16:31 pm: How do I do this?

A trailer of mass 300kg is being towed on a level road by a car mass 1000kg. There is a constant retarding force, due to air resistance and friction, of 90N on the trailer, and 400N on the car. The vehicles are travelling at a constant speed.
What is the:
a. value of the tension, T, in the towbar?
b. magnitude of the force driving the car?
c. How far will the car and trailer travel before coming to rest?
Title: Re: Kinda weird
Post by: /0 on January 19, 2010, 12:07:21 am: Draw free body diagrams for each vehicle.
(By the way it was not necessary to draw the vertical forces - which is especially annoying when you have wheels...
$N_1+N_2 = 300g$ , $N_3+N_4 = 1000g$ , but I included them for completeness)

a) Use $F_{net} = 0$ on the trailer.

b) Use $F_{net} = 0$ on the car.

c) Until the fuel runs out.

Nah, the question is worded badly. Probably means after the engine is turned off. Only thing is it's missing the speed...

Oh well, total retarding force (on the whole system) is $490\ \mbox{N}$

Then use $F \Delta t = m \Delta v$

Solving should give $t = \frac{130}{49}v$
Title: Re: Kinda weird
Post by: kenhung123 on January 19, 2010, 12:18:23 am: I'm assuming c means distance but since a=0 wouldn't distance be zero?
Title: Re: Kinda weird
Post by: /0 on January 19, 2010, 12:58:03 am: Ah crap, read it wrong. Yeah but they are travelling at constant speed so they shouldn't even slow down.
Title: Re: Kinda weird
Post by: superflya on January 19, 2010, 02:10:53 pm: constant retarding force & constand speed ? wtf
Title: Re: Kinda weird
Post by: /0 on January 19, 2010, 03:48:15 pm: The driving force opposes the retarding force exactly so that it stays at constant speed.
Title: Re: Kinda weird
Post by: superflya on January 19, 2010, 05:56:24 pm: lol -.- ahhhk