Question

A single block brake with a short shoe and torque capacity of 250 Nm is shown. The cylindrical brake drum rotates anticlockwise at 100 rpm and the coefficient of friction is 0.25. The value of a in mm (round off to one decimal place), such that the maximum actuating force P is 2000 N is

• A. 212.5

Answer 1

The correct option is A 212.5

Drum eq.

$\therefore T_f=\mu R_N.a$

$250=0.25\times R_N\times a\left(i\right)$

Lever eq.

$P\times 2.5a-\mu R_N=\frac{a}{4}-R_N\times a=0$

$R_N(1+\frac{0.25}{4})=2000\times 2.5$

$R_N=4705.882N..\left(ii\right)$

By eq.(i)

$250=0.25\times 4705.882\times a$

$a=212.5mm$