Question

A wrench with a length of `63 cm` is being used to unscrew a `7/2 cm` bolt. If a torque of `18 Nm` is needed to overcome the friction keeping the bolt in place, what is the minimum torque that must be applied to the wrench to unscrew the bolt?

Answer 1

Given:

`tau = 18"N"*"m"`
`r = 0.63"m"`

We will take the axis of rotation to be the bolt, its parameters are relatively irrelevant. Moreover, assume that the force we exert on the wrench is perpendicular to the lever arm, `r`.

Recall,

`tau = r*F*sintheta`

Hence, a,

`18"N" * "m" = 0.63"m" * F * 1`

`therefore F approx 29"N"`

force must be applied to that wrench to achieve the torque required to "unscrew" the bolt.

Answer 2

The minimum torque that must be applied to the wrench is given in the question: `18 N*m`.