Machine Design
Which of the following statement is correct regarding power screws?

If the friction angle is less than the helix angle of the screw, then the efficiency will be more than 50%
The efficiency of Acme (trapezoidal) thread is less than that of a square thread
The efficiency of a self locking screw can not be more than 50%
Both (A) and (B)

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Machine Design
In a band and block brake, the ratio of tensions on the tight and slack sides of band is given by (where μ = Coefficient of friction between the blocks and the drum, θ = Semi-angle of each block subtending at the centre of drum, and n = Number of blocks)

T₁/T₂ = (μθ)n
T₁/T₂ = [(1 - μ tanθ)/ (1 + μ tanθ)]n
T₁/T₂ = μθ × n
T₁/T₂ = [(1 + μ tanθ)/ (1 - μ tanθ)]n

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