Theory of Machines - GATE practice papers - Mechanical

1)   Which of the following statements is wrong?

(1) A statically balanced rotor is always dynamically balanced
(2) A dynamically balanced rotor is always statically balanced (Marks: 02)

- Published on 19 Oct 15

a. Only (1)
b. Only (2)
c. both (1) and (2)
d. both are correct
Answer  Explanation 

ANSWER: Only (1)

Explanation:
When rotor is dynamically balanced then it is always statically balanced. But when rotor is statically balanced then it may or may not be dynamically balanced.


2)   The punching rate of a punching press is 20 holes per minute. It is required to punch a hole of diameter 50 mm on a plate of 20 mm thickness. Press requires 10 N-m of energy per mm2 of sheared area. Calculate the energy required for punching work per second. (Marks: 02)
- Published on 19 Oct 15

a. 628318.2 Nm/s
b. 10471.97 Nm/s
c. 31416 Nm/s
d. none of the above
Answer  Explanation 

ANSWER: 10471.97 Nm/s

Explanation:
d =50 mm
t = 20 mm
Number of holes = 20 holes per minute
Energy required = 10 N-m/mm 2

Sheared area per hole = πdt
= π × 50 × 20
= 3141.6 mm2

Energy required to punch one hole = 3141.6 × 10
= 31416 N-m

and the energy required for punching work per second
= energy required per hole × number of holes per second
= 31416 × (20/60)
= 10471.97 Nm/s


3)   How is the kinematic pair formed?(Marks: 01)
- Published on 19 Oct 15

a. when two kinematic links of a machine are in contact with each other and relative motion between them is not completely constrained
b. when two kinematic links of a machine are in contact with each other and relative motion between them is completely constrained
c. both a. and b.
d. none of the above
Answer  Explanation 

ANSWER: when two kinematic links of a machine are in contact with each other and relative motion between them is completely constrained

Explanation:
When two kinematic links or elements are in contact with each other, they are said to form a pair and if the relative motion between them is completely constrained, the pair is called as kinematic pair.


4)   The part of machine which is resistant and undergoes relative motion is called as __________(Marks: 01)
- Published on 19 Oct 15

a. kinematic link
b. element
c. both a. and b.
d. none of the above
Answer  Explanation 

ANSWER: both a. and b.

Explanation:
A part of machine which undergoes relative motion with respect to some other part is called as as kinematic link or element. The kinematic link or element should be resistant body.


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