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ISRO 2014 Mechanical Engineering Questions, Answers and Explanation

ISRO 2014 Mechanical Engineering Questions, Answers and Explanation

18. Tension in the cable supporting a lift of weight 'W' and having an acceleration 'a' while going upward is (g is acceleration due to gravity)
a) W(1+a/g)
b) W(1-a/g)
c) W(2+a/g)
d) W(1+2a/g)

Answer
a) W(1+a/g)

Explanation [Engineering Mechanics]
Tension increases when the lift accelerate upwards and decreases when the lift accelerate downwards.
Mass of the lift = W/g
Increase in tension due to acceleration = mass of list * acceleration of lift = W/g*a
Total tension = Tension due to gravity + Tension due to acceleration
 = W + W/g*a = W(1+g/a)

2014. 80. Which type of gear meshing should be employed to transmit torque to a linear force?
a) Epicyclic gear
b) Helical gear
c) Bevel gear
d) Rack and pinion
Answer
d) Rack and pinion
Explanation [Theory of Machines and Mechanical Vibrations]
Epicyclic gear trains have one or more axes of gears in motion. In all other gear types the gear rotates about an axis but the axis does not move.
Helical gears are smoother in operations and create a thrust load and hence required support to compensate this load. They can also be used to transmit torques at 90o 
Bevel gears are the ones in which the axes of gears intersect normally at 90o. But they can work at other angles also.
Rack and pinion gears are used to convert rotation into linear motion.


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