# Machine Design Questions and Answers – Block Brake

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This set of Machine Design Multiple Choice Questions & Answers (MCQs) focuses on “Block Brakes”.

1. Block brakes are never used in railway trains.
a) True
b) False

Explanation: Blocks brakes are commonly employed in railway trains.

2. If torque capacity of a block brake is 240N-m and radius of drum is 210mm with coefficient of friction 0.4.
a) None of the listed
b) 2857.14N
c) 3443.42N
d) 2334.62N

Explanation: N=M/μR.

3. If initially drum of radius 200mm is rotating at 100rpm, then calculate the heat generated if frictional force acting is 1140N.
a) 3345W
b) 4456W
c) 5969W
d) 11938W

Explanation: Heat=Frictional forcexaverage velocity.

4. In a block brake with short shoe, it is assumed that friction force and normal reaction are concentrated at the midpoint of the shoe.
a) True
b) False

Explanation: The angle of contact is less than 45⁰ and hence the assumption is valid.

5. The pressure intensity at an element on long shoe brake varies directly with the sin of the pressure angle of the element of friction lining.
a) True
b) False

Explanation: p=Cxcos(Ǿ).

6. The equivalent coefficient of friction in case of block brake with long shoe is denoted by μ[4Sinθ/2θ+sin4θ].
a) True
b) False

Explanation: μ[4Sinθ/2θ+sin2θ].

7. In pivoted block brakes, moment of frictional force about pivot is non zero.
a) True
b) False

Explanation: Pivot point is selected such that moment of frictional force about pivot point is zero.

8. Shoe is constrained to move towards the drum to compensate for the moment acting.
a) Yes
b) It compensates for wear
c) It compensates for both wear and moment
d) None of the listed

Explanation: It compensates for the wear which is constant for all points.

9. A pivoted double block brake has a drum radius of 280mm with two shoes subtending an angle of 100⁰. Calculate the distance of pivot from axis of drum.
a) 321.5mm
b) 314.3mm
c) 289.5mm
d) None of the mentioned

Explanation: h=4Rsinθ/2θ+sin2θwhere θ=100/2.

10. A pivoted double block brake has a drum radius of 280mm with two shoes subtending an angle of 100⁰. Maximum pressure intensity is 0.5N/mm². If the width of friction lining is 90mm, find the torque capacity f each shoe. Assume coefficient of friction as 0.2.
a) 789N-m
b) 1081N-m
c) 945N-m
d) None of the listed

Explanation: M=2μR²wpsinθ.

11. A pivoted double block brake has a drum radius of 280mm with two shoes subtending an angle of 100⁰. Maximum pressure intensity is 0.5N/mm². If the width of friction lining is 90mm, find the reaction at pivot in horizontal direction. Assume coefficient of friction as 0.2.
a) None of the listed
b) 21123N
c) 17200N
d) 16789N

Explanation: R(x)=Rwp(2θ+sin2θ)/2.

12. A pivoted double block brake has a drum radius of 280mm with two shoes subtending an angle of 100⁰. Maximum pressure intensity is 0.5N/mm². If the width of friction lining is 90mm, find the reaction at pivot in horizontal direction. Assume coefficient of friction as 0.2.
a) None of the listed
b) 2113N
c) 1720N
d) 3440N  