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## Homework Statement

Just asking for a little help on this question

50kg object is pulled across a rough horizontal surface with a uniform force of 250N for 15m from rest, the surface has a frictional coefficient of 0.4, calculate the acceleration using dealemberts principle

But this results in a minus answer, so I'm lost, any help would be appreciated!

## Homework Equations

Conservation of energy, d'alemberts principle

## The Attempt at a Solution

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I have worked out the acceleration using conservation of energy using

PE+KE+Win = PE+KE+Wout+losses

To find the final velocity, and used

a=v^2-u^2/2s

To find acceleration which comes to 1.08m/s^2

Now the other part of the question is use d'alemberts principle to solve the same problem but I cannot for the life of me work this out, it's probably really simple but I just can't see it

I thought I would go down the route of force in minus the forces against = 0 to find the inertia force and use that to find acceleration, with F = -ma

But this results in a minus answer, so I'm lost, any help would be appreciated!