Question

A firefighter needs to adjust the valve on a fire hydrant to regulate the flow of water. She attaches a wrench to the bolt of the valve. How should she apply force to the wrench in order to get the most torque on the bolt?

Answer 1

We know Torque $\vec{T}$ = $\vec{r}\times \vec{F}$

where F is the applied force , r is the perpendicular distance between applied force and axis of rotation.

also $\vec{T}$ = rFsin $\theta$

to be torque maximum $\theta$ should be 90⁰ (As sin90 is the maximum=1).

and r should be maximum.

So the force applied on the wrench should be Perpendicular to the length of the wrench and far from the bolt.