A particular bridge, with a length L , consists of a horizontal slab with a weig

Question

A particular bridge, with a length L, consists of a horizontal slab with a weight of 48.0 kN, with the weight uniformly distributed. The slab is held up by one support 20% of the way across the bridge, and a second support 80% of the way across the bridge. As shown in the picture, a truck with a weight of mg = 21.0 kN is driving from left to right across the bridge.

1) At the instant the truck’s weight is directly above the right support, what is the magnitude of the force the right support exerts on the horizontal slab?

______________kN

2) As the truck continues to drive to the right across the bridge, what will happen to the magnitudes of the support forces? Select all the correct statements, assuming the truck is entirely on the bridge.

Explanation / Answer

1) as the system is in equilibrium therefore moment about left support will be zero
48*0.3+21*0.6-Fright*0.6=0

Fright=45 N

2)The right support force will increase

48*0.3-21*x-Fleft*0.6=0

and

The left support force will decrease.

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