# Help with Mechanics

1. Sep 18, 2010

### Doubell

1. The problem statement, all variables and given/known data

a car of 1000kg tows a caravan of mass 600kg up a road which rises 1 m vertically for every
20 m of its lenght. there are constant frictional resistant forces of 200 N and 100 N to the motion of the car and the motion of the caravan respectively. the combination has an acceleration of 1.2 m/s^2 with the engine exerting a constant driving force. find (a) the driving force, (b) the tension in the tow bar. (g= 10 m/s^2)

2. Relevant equations

F=m*a

3. The attempt at a solution

using F=m*a i multiplied the combined mass (1600kg) * 1.2 m/s^2 and got 1920 N i dont think that is right the method seems to be too easy plus i know that something about the rising of the road by 1m for every 20m of its lenght should be used to calculate the driving force as for the tension i dont know how to start it

2. Sep 18, 2010

### PhanthomJay

Re: Mechanics

Remember it is not F=ma, it's F_net =ma. That means the net force up the plane is 1920N. You need to draw a free body diagram of the car-caravan system to find all the forces acting on the system. Along (parallel to) the incline, the driving force is just one of those forces. What are the others , and in what direction to they act? The algebraic sum of those forces is the NET force acting up the incline. (Hint: there are also friction and components of the gravity forces acting along the incline).

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