Crowbar - lever

How much force must we apply to the end of a 2.4 m long crowbar to lift a door weighing 220 kg, if it stands on the crowbar 35 cm from its end, which is resting on the ground?

Correct answer:

F₂ =  314.7375 N

Step-by-step explanation:

$$\begin{gathered} a=2.4\text{m} \\ b=35\text{cm}\to \text{m}=35:100\text{m}=0.35\text{m} \\ m=220\text{kg} \\ g=9.81{\text{m/s}}^2 \\ {F}_1=m\cdot g=220\cdot 9.81=\frac{10791}{5}=2158.2\text{N} \\ {M}_1=M_2 \\ {F}_1\cdot b=F_2\cdot a \\ {F}_2=F_1\cdot \frac{b}{a}=2158.2\cdot \frac{0.35}{2.4}=314.7375\text{N} \end{gathered}$$

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