How Do I Solve These Torque Diagram Problems?

[orgo]

I'm stuck on these problems!

1. Suppose a 90.0-g mass is placed at the 82.0 cm mark of a 120.0 g uniform meterstick. At what mark will the meterstick balance?

For this problem, I did TCCW=TCW. I think the TCW is (90 g)*(9.8 m/s^2)*(32 cm). For TCCW, I am not sure because I do not know where the pivot point is.

2. A 10,000 kg bridge of length 10 m is supported at both ends. If a 2000-kg car is parked on the bridge 3.0 m from the left support, what are the supporting forces at the left and right ends?

I drew a diagram for this problem, but I do not know how to calculate the supporting forces.

 

[jepe]

set up the momentum balance about the zero mark of the meterstick:
90*9.8*82+120*9.8*50-210*9.8*x=0
210 (=90+120)*9.8 being the reaction force at the pivotpoint
x = the distance of the pivot point from the zero mark
work out x and you have the answer for question 1.

 

[Doc Al]

bridge problem

2. A 10,000 kg bridge of length 10 m is supported at both ends. If a 2000-kg car is parked on the bridge 3.0 m from the left support, what are the supporting forces at the left and right ends?

I drew a diagram for this problem, but I do not know how to calculate the supporting forces.

Identify all the forces acting on the bridge: its weight, the weight of the car, the left supporting force, and the right supporting force. Draw these on your diagram.

Now apply the conditions for equilibrium:
(1) The forces must balance
(2) The torques about any point must balance

Give it a shot.