(adsbygoogle = window.adsbygoogle || []).push({}); 1. The problem statement, all variables and given/known data

A particle P of mass 4 kg moves along a horizontal straight line under the action of a force directed towards a fixed point O on the line. At time t seconds, P is x metres from O and the force towards O has magnitude 9x newtons. The particle P is also subject to air resistance, which has magnitude 12v newtons when P is moving with speed v m/s.

Show that the equation of motion of P is:

[tex]4\frac{d^{2}x}{dt^2} + 12\frac{dx}{dt} + 9x = 0[/tex]

2. Relevant equations

F = ma

3. The attempt at a solution

The only way you get this is if you take 12v and 9x to be acting in the same direction. But how can they be? Surely they must be opposite? If I just resolve it assuming they act in opposite directions I get a sign error. Can anyone help me?

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# Homework Help: Resolving Forces

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