A uniform bridge span weighs 80.0 × 10³ N and is 30.0 m long.An automobile weighing 12.0 × 10³ N is parked with its center of gravity located 12.0 m from the right pier.What upward support force does the right pier provide? A) 44.8 × 10³ N B) 54 × 10³ N C) 32.8 × 10³ N D) 47.2 × 10³ N E) 46 × 10³ N

Question

Quizplus · Accepted Answer

We can use the principle of moments to find the upward support force provided by the right pier. Taking moments about the left pier,
$$
	ext{Clockwise moment} = 	ext{Anticlockwise moment}
$$
$$
F_R\cdot 30 = 12	imes 10^{10}\cdot 18
$$
where $F_R$ is the upward support force provided by the right pier. Solving for $F_R$ gives $F_R = 47.2 	imes 10^{10} 	ext{ N}$. Therefore, the correct answer is D.

A Uniform Bridge Span Weighs 80