GATE 2019 ME (ME2) – Question 52
The shown short-shoe external drum brake has drum diameter 500 mm and dimensions a = 1000 mm, b = 500 mm, c = 200 mm. Friction coefficient is 0.35. Force F = 100 N is applied as shown; the drum rotates anticlockwise. Find braking torque (N·m), to two decimal places.
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Correct answer: 19 to 21
Explanation
At the top of an anticlockwise drum, friction on the shoe acts left. Its point of application is above the pivot, so friction assists the applied-force moment. Thus $Fa=N(b-\mu c)$. Then $N=100(1000)/(500-0.35\cdot200)=232.558$ N. Braking torque is $\mu ND/2=0.35(232.558)(0.25)=\mathbf{20.35}$ N·m.