Question

The block brake consists of a pin-connected lever and friction block at B. The coefficient of static friction between the wheel and the lever is μs = 0.3, and a torque of 5 N⋅m is applied to the wheel. Determine if the brake can hold the wheel stationary when the force applied to the lever is (a) P = 30 N, (b) P = 70 N.

Answer 1

Answer:

B

Explanation:

Answer 2

Answer:

a) Insufficient

b) Sufficient

Explanation:

To hold lever:

Sum of moments about point O center of wheel = 0

Fb * 0.15 - 5 =0

Fb = 33.33N

Contact force Nb:

Nb = (Fb/u) = (33.333 / 0.3) = 111.1 N

Sum of moments about point A lever pin joint = 0

Preq * 0.6 - 111.1*0.2 - 33.33*0.05 = 0

Preq = 39.8 N

part a

P = 30N < Preq = 39.8N

Hence, insufficient

part b

P = 70N > Preq = 39.8N

Hence, sufficient