1. The problem statement, all variables and given/known data 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! 2. Relevant equations Conservation of energy, d'alemberts principle 3. The attempt at a solution 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!