The bridge from problem 3 needs to draw up the
> leaves to let a ship through. The leaves are being lifted when someone
> notices a truck has broken down on one leaf and cannot be moved. It takes
> some time to stop the motor that controls the lift of the leaf. By how much
> can the truck be lifted by the leaf of the bridge before it starts to roll
> back? Assume the coefficient of static friction between the leaf surface and
> truck is 0.2. In your answer report the angle of the leaf of the bridge at
> the point just before the truck will roll. When justifying your answer use a
> free body diagram and appropriate working.

PLEASE HELP!!

Draw up a free body diagram, just as the problem suggests. You are interested specifically in the forces acting in the direction parallel to the tilted bridge surface. There are two forces that just balance out each other for the truck to be on the verge of slipping:

1. Force due to gravity that causes it to slide down the slope - equal to the component of the truck's weight that is parallel to the sloped surface, and
2. Force due to friction that opposes this force. Friction force is modeled as the componentof the truck's weight that is normal to the sloped surface times the coefficient of friction.

Set these equal, and let us know what you get for the angle of the bridge.