Class-3 Lever: Numerical Example

In a Class 3 Lever, we are given the following information:

L1 = 1 ft

L2 = 3 ft

Weight at one end of the lever is 300 lb.

We are required to calculate the following:

a. Mechanical advantage for this lever.

b. Force required necessary at the other end of the lever to lift the 500 lb weight.

Solution

a. MA = 1/3 = 0.33

b. To lift the weight, F2 must be equal to 300 lb weight. Therefore F2 = 300 lb. Now we need to calculate F1.

F1 = F2/MA = 300/0.33 = 909 lb.