A large crate weighing 5416 N rests on four 12-cm-high blocks on a horizontal su

Question

A large crate weighing 5416 N rests on four 12-cm-high blocks on a horizontal surface (figure below). The crate is 2.0 m long, 1.2 m high, and 1.2 m deep. You are asked to lift one end of the crate using a long steel pry bar. The fulcrum on the pry bar is 9 cm from the end that lifts the crate. Estimate the length of the bar you will need to lift the end of the crate. (Assume the maximum force you can apply is 500 N and that the pry bar is massless. Also assume that the bend in the pry bar is negligible.)

Answer in cm...

Explanation / Answer

Equating torques about the left end at which the pry exerts force on the crate,

5416*(1) = N2*(2)

So, N2 = 2708 N

where N2 = normal force from the right side blocks

N1 = normal force from the pry bar

Equating forces in vertical:

5416 = N2 + N1*(0.12/sqrt(0.12^2+0.09^2))

So, N1 = 3385 N

So, For the fulcrum, writing torque equation:

L*500 = N1*sqrt(0.09^2+0.12^2)

So,L*500 = 3385*sqrt(0.09^2+0.12^2)

So, L = 1.016 m = 101.6 cm <---------answer

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