Engineering Questions with Answers - Multiple Choice Questions
Machine Kinematics MCQ – Belt, Rope and Chain Drives
The velocity ratio of two pulleys connected by an open belt or crossed belt is
a) directly proportional to their diameters
b) inversely proportional to their diameters
c) directly proportional to the square of their diameters
d) inversely proportional to the square of their diameters
Explanation: It is the ratio between the velocities of the driver and the follower or driven.
Let d1 = Diameter of the driver,
d2 = Diameter of the follower,
N1 = Speed of the driver in r.p.m., and
N2 = Speed of the follower in r.p.m.
∴ Length of the belt that passes over the driver, in one minute
= π d1.N1
Similarly, length of the belt that passes over the follower, in one minute
= π d2 . N2
Since the length of belt that passes over the driver in one minute is equal to the length of belt that passes over the follower in one minute, therefore
π d1.N1 = π d2 . N2
∴ Velocity ratio, N2/N1 = d1/d2.
Two pulleys of diameters d1 and d2 and at distance x apart are connected by means of an open belt drive. The length of the belt is
a) π /2 (d1 + d2) 2x + (d1 + d2)2/4x
b) π /2 (d1 – d2) 2x + (d1 – d2)2/4x
c) π /2 (d1 + d2) 2x + (d1 – d2)2/4x
d) π /2 (d1 – d2) 2x + (d1 + d2)2/4x
In a cone pulley, if the sum of radii of the pulleys on the driving and driven shafts is constant, then
a) open belt drive is recommended
b) cross belt drive is recommended
c) both open belt drive and cross belt drive are recommended
d) the drive is recommended depending upon the torque transmitted
Explanation: In a cross belt drive, both the pulleys rotate in opposite directions. If sum of the radii of the two pulleys be constant, then length of the belt required will also remain constant, provided the distance between centres of the pulleys remain unchanged.
Due to slip of the belt, the velocity ratio of the belt drive
c) does not change
d) none of the mentioned
Explanation: The result of the belt slipping is to reduce the velocity ratio of the system. As the slipping of the belt is a common phenomenon, thus the belt should never be used where a definite velocity ratio is of importance.
When two pulleys of different diameters are connected by means of an open belt drive, then the angle of contact taken into consideration should be of the
a) larger pulley
b) smaller pulley
c) average of two pulleys
d) none of the mentioned
The power transmitted by a belt is maximum when the maximum tension in the belt (T) is equal to
Explanation: When the power transmitted is maximum, 1/3rd of the maximum tension is absorbed as centrifugal tension.
T = 3TC
where TC = Centrifugal tension.
The velocity of the belt for maximum power is
Explanation: We know that T1 = T– TC and for maximum power TC = T/3
T1 = T – T/3 = 2T/3
the velocity of the belt for the maximum power, v = √T/3m
where m = Mass of the belt in kg per metre length.
The centrifugal tension in belts
a) increases power transmitted
b) decreases power transmitted
c) have no effect on the power transmitted
d) increases power transmitted upto a certain speed and then decreases
When the belt is stationary, it is subjected to some tension, known as initial tension. The value of this tension is equal to the
a) tension in the tight side of the belt
b) tension in the slack side of the belt
c) sum of the tensions in the tight side and slack side of the belt
d) average tension of the tight side and slack side of the belt
Explanation: When the driver starts rotating, it pulls the belt from one side (increasing tension in the belt on this side) and delivers it to the other side (decreasing the tension in the belt on that side). The increased tension in one side of the belt is called tension in tight side and the decreased tension in the other side of the belt is called tension in the slack side.
The relation between the pitch of the chain ( p) and pitch circle diameter of the sprocket (d) is given by
a) p = d sin (600/T)
b) p = d sin (900/T)
c) p = d sin (1200/T)
d) p = d sin (1800/T)
Explanation: It is given by p = d sin (1800/T).