# Engineering Mechanics – Section 3

41. For a self-locking machine, the efficiency must be

A. equal to 50%
B. less than 50%
C. greater than 50%
D. 100%

Correct Answer: B. less than 50%

42. The resultant of the two forces P and Q is R. If Q is doubled, the new resultant is perpendicular to P. Then

A. P = Q
B. Q = R
C. Q = 2R
D. none of these

Correct Answer: B. Q = R

43. One joule is equal to

A. 0.1 N-m
B. 1 N-m
C. 10 N-m
D. 100 N-m

44. Whenever a force acts on a body and the body undergoes a displacement, then

A. work is said to be done
B. power is being transmitted
C. body has a kinetic energy of translation
D. none of these

Correct Answer: A. work is said to be done

45. When a particle moves along a straight path, there will be centripetal acceleration as well as tangential acceleration.

A. Correct
B. Incorrect

46. If the body falls freely under gravity, then the gravitational acceleration is taken as

A. +8.9 m/s2
B. -8.9 m/s2
C. +9.8 m/s2
D. -9.8 m/s2

47. A framed structure, as shown in the below figure, is a A. perfect frame
B. deficient frame
C. redundant frame
D. none of the above

48. The rate of change of displacement of a body is called

A. velocity
B. acceleration
C. momentum
D. none of these

49. The efficiency of a screw jack is maximum, when(where α = Helix angle, and φ = Angle of friction.)

A. α = 45° + φ/2
B. α = 45° – φ/2
C. α = 90° + φ
D. α = 90° – φ

Correct Answer: B. α = 45° – φ/2

50. The periodic time (T) is given by(where ω = Angular velocity of particle in rad / s.)

A. ω/2π
B. 2π/ω
C. 2π x ω
D. π/ω