# Machine Kinematics Questions and Answers – Friction Clutches

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This set of Machine Kinematics Multiple Choice Questions & Answers (MCQs) focuses on “Friction Clutches”.

1. A jaw clutch is essentially a
a) positive action clutch
b) cone clutch
c) friction clutch
d) disc clutch

Explanation: The positive clutches are used when a positive drive is required. The simplest type of a positive clutch is a jaw or claw clutch.

2. The material used for lining of friction surfaces of a clutch should have _____________ coefficient of friction.
a) low
b) high
c) medium
d) none of the mentioned

Explanation: The material should have a high and uniform coefficient of friction.

3. The torque developed by a disc clutch is given by
a) T = 0.25 µ.W.R
b) T = 0.5 µ.W.R
c) T = 0.75 µ.W.R
d) T = µ.W.R

Explanation: T = µ.W.R
where W = Axial force with which the friction surfaces are held together ;
µ = Coefficient of friction ; and
R = Mean radius of friction surfaces.
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4. In case of a multiple disc clutch, if n1 are the number of discs on the driving shaft and n2 are the number of the discs on the driven shaft, then the number of pairs of contact surfaces will be
a) n1 + n2
b) n1 + n2 – 1
c) n1 + n2 + 1
d) none of the mentioned

Explanation: If n1 are the number of discs on the driving shaft and n2 are the number of the discs on the driven shaft, then the number of pairs of contact surfaces will be
n1 + n2 – 1.

5. The cone clutches have become obsolete because of
a) small cone angles
b) exposure to dirt and dust
c) difficulty in disengaging
d) all of the mentioned

Explanation: A cone clutch, was extensively used in automobiles, but now-a-days it has been replaced completely by the disc clutch. In a cone clutch, the driver is keyed to the driving shaft by a sunk key and has an inside conical surface or face which exactly fits into the outside conical surface of the driven.

6. The axial force (We) required for engaging a cone clutch is given by
a) Wn sin α
b) Wn (sin α + µ cos α )
c) Wn (sin α + 0.25 µ cos α )
d) none of the mentioned

Explanation: Axial force required for engaging the clutch = Wn (sin α + 0.25 µ cos α )
where Wn = Normal force acting on the contact surfaces,
α = Face angle of the cone, and
µ = Coefficient of friction.

7. In a centrifugal clutch, the force with which the shoe presses against the driven member is the ___________ of the centrifugal force and the spring force.
a) difference
b) sum
c) ratio
d) none of the mentioned

Explanation: The force with which the shoe presses against the driven member is the difference of the centrifugal force and the spring force. The increase of speed causes the shoe to press harder and enables more torque to be transmitted.

8. Centrifugal clutches are designed to provide automatic and smooth engagement of load to driving member.
a) True
b) False

Explanation: Since the operating centrifugal force is a function of square of angular velocity, the friction torque for accelerating a load is also a function of square of speed driving member.

9. For a power screw having square threads with lead angle of 450 and coefficient of friction of 0.15 between screw and nut, the efficiency of the power screw, neglecting collar friction, is given by
a) 74%
b) 64%
c) 54%
d) 44%

Explanation: ȵ = tanα/tan(α + ɸ)
ɸ = angle of friction,
α = Helix angle or lead angle
tanɸ = 0.15
ɸ = 8.530
ȵ = 74% .
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