. 30

• A l-m pry bar is held horizontally and used to open a crate. The tip of the

bar, which serves as the fulcrum, is pushed in a distance of 2 cm between

the crate lid and the crate. If a 20-N force is applied perpendicularly to the

end of the bar, what force is applied on the crate lid?

(A) IN

(B) 100 N

(C) 10 N

(D) 1,000 N

(E) 10,000 N

Explanation:

Length if the bar is 1m=100cm

The tip of the bar serves as fulcrum

A force of 20N (upward) is applied at the tip of the other end. Then, the force is 100cm from the fulcrum

The crate lid is 2cm from the fulcrum, let the force (downward) acting on the crate be F.

Using moment

Sum of the moments of all forces about any point in the plane must be zero.

Let take moment about the fulcrum

100×20-F×2=0

2000-2F=0

2F=2000

Then, F=1000N

The force acting in the crate lid is 1000N

Option D is correct

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