Can someone show and explain why d is the answer? The free body diagram below re
ID: 1314813 • Letter: C
Question
Can someone show and explain why d is the answer?
The free body diagram below represents a 1 500 kg car sitting on a 3 000 kg bridge supported at its far ends. The car's position is three quarters of the length L from the left end of the bridge. Identify the one error in the torque equation below:
a.
never produces a torque on the bridge no matter where the axis of rotation is placed.
b.
never produces a torque on the bridge no matter where the axis of rotation is placed.
c.
cannot produce a torque on the bridge no matter where the axis of rotation is taken since it is at the center of the bridge.
d.
Because the perpendicular distance to from the left end of the bridge is 0, F1L should be 0.
e.
Because the perpendicular distance to from the right end of the bridge is 0, F2L should be 0.
ANS: D PTS: 3 DIF: Challenging
a.
never produces a torque on the bridge no matter where the axis of rotation is placed.
b.
never produces a torque on the bridge no matter where the axis of rotation is placed.
c.
cannot produce a torque on the bridge no matter where the axis of rotation is taken since it is at the center of the bridge.
d.
Because the perpendicular distance to from the left end of the bridge is 0, F1L should be 0.
e.
Because the perpendicular distance to from the right end of the bridge is 0, F2L should be 0.
Explanation / Answer
Torque is distance from reference Force * force
from the free body diagram we took our refernce force as F1
as distance from F(earth on bridge) to F1 is 0.5L and - ve sign as force is down, torue = -0.5*L*F1
similarly distance from F(earth on car) to F1 is 0.75L and - ve sign as force is down,torue = -0.75*L*F1
and distance from F2 to F1 is L and + ve sign as force is up, torue = L*F1
but distance from F1to F1 is 0 and so torque becomes F1*0 = 0