25. A student is removing rocks from a garden. She exerts a force of 218 N on a lever to raise one rock a distance of 11.0 cm.
a. If the rock weighs 1050 N, how far does the girl move her end of the lever if the lever is an ideal machine?
b. If the lever actually has an efficiency of 78.3 percent, how far does the girl move her end of the lever?

a) 53.0 cm

b) 67.7 cm

Explanation:

a)

In an ideal lever (100% efficiency), the work done in input is equal to the work done in output. So we can write:

And both works can be rewritten as

where

is the force in input

is the force in output

is the effort arm

is the load arm

Here we have:

is the force exerted in input

is the output force (the weight of the rock)

is the distance through which the rock is lifted

So, we can find the distance through which the lever moves on the input end:

b)

In this case, the lever has an efficiency of

Efficiency can be rewritten as the ratio between output work and input work:

The output work is

Therefore the input work is

This input work can be rewritten as

And so we can find by how much the girl moves her end of the lever in this case:

r=rho l/a where a is the area, l is the length and rho is resistivity so the greater the area the lesser the resistance thats why the earth pin is thicker bcos current follow the shortest path, so less resistive .

correct it is c.) b b