Question

A bridge is supported by two piers located 12 meters apart. Both the left and right piers provide an upward force on the bridge, labeled FL and FR respectively.

a. If a 1700 kg car comes to rest at a point 5 meters from the left pier, how much force (in N) will the bridge provide to the left and right piers? (Enter the magnitudes.)

F_L = N

F_R =   N

How will F_L and F_R change as the car drives to the right side of the bridge?

A. As the car moves to the right side of the bridge, F_L will increase and F_R will decrease.

B. As the car moves to the right side of the bridge, both F_L and F_R will decrease.     

C. As the car moves to the right side of the bridge, both F_L and F_R will increase.

D. As the car moves to the right side of the bridge, F_L will decrease and F_R will increase.

Answer 1

distance apart the piers = 12 m

weight of the car = 1700g = 16660 N

distance the car from left = 5 m

taking moments about left pier

M = F_R *12 - 16660 *5 =0

F_R = 6942 N

taking moments about the right pier

M = F_L *12 - 16660 *(12-5) =0

F_L = 9718 N

b) (D) - As the car moves to the F_R increases and F_L decreases.

distance of the load from the right decrease hence F_r increases