A brake-block shown below has a face width of 300 mm. 

GATE - 2007 M.E Images Q49

The mean coefficient of friction is 0.25. For an activating force of 400 N, the braking torque in Nm is

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ISRO VSSC Technical Assistant Mechanical 14 July 2021 Official Paper
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  1. 30
  2. 40
  3. 45
  4. 60

Answer (Detailed Solution Below)

Option 3 : 45
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Detailed Solution

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Explanation:

Free body diagram of lever and brake dram are

GATE - 2007 M.E Images Q49a

For lever moment about O, ∑Mo = 0

⇒ (400 N) × (400 + 200) mm = N × 200 mm

\(\Rightarrow Normal\;force,\;N = \frac{{400 \times 600}}{{200}} = 1200\;N\)

Tangential force, Ft = μN = 0.25 × 1200 = 300 N

Braking torque = Tb = Ft × r = 300 × 0.15 = 45 N.m

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