Question

A heavy uniform plank of length L is supported by two force F, and F2 at points distant
and from its ends as shown in the diagram. What is the ratio of F1 to Fz?
plank
E
A) 2:5
B) 3:5
C) 5:8
D) 2:3​

Answer 1

Answer: D) 2:3

Explanation:

This is a torque problem. To balance the plank, the counter clockwise torque must be equal to the clockwise torque. To simplify this problem, let’s assume the length of the plank is 8 meters. The left support is 1 meter from its left end.

L/4 = 2 meters

The right support is 2 meters from the right end. Let the pivot point be at the center of the plank. F1 is 3 meters from this point. F2 is 2 meters from this point.

Counter clockwise torque = F2 * 2

Clockwise torque = F1 * 3

F1 * 3 = F2 * 2

F1/F2 = 2/3

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