Question

A block-brake shown below has a face width of 300 mm and a mean coefficient of friction of 0.25. For an activating force of 400 N, the braking torque in Nm is

• A. $40$
• B. $45$
• C. $60$
• D. $30$

Answer 1

The correct option is B $45$


Since, it is in equilibrium, moment about $A$ should be zero
Taking moment about point $A$,
$\sum M_A=N\times 200-400\times 600=0$

$N=1200N$
$f=\mu N=0.25\times 1200=300N$

$\text{Braking torque}=f\times 150$

$\frac{300\times 150}{1000}=45Nm$