# Engineering Mechanics – Section 6

31. For any system of coplanar forces, the condition of equilibrium is that the

A. algebraic sum of the horizontal components of all the forces should be zero
B. algebraic sum of the vertical components of all the forces should be zero
C. algebraic sum of moments of all the forces about any point should be zero
D. all of the above

Correct Answer: D. all of the above

32. The ratio of static friction to dynamic friction is always

A. equal to one
B. less than one
C. greater than one
D. none of these

Correct Answer: C. greater than one

33. A science teacher claimed that Newton’s third law of motion is involved while studying the motion of rockets. His statement is

A. justified
B. not justified

34. One kg force is equal to

A. 7.8 N
B. 8.9 N
C. 9.8 N
D. 12 N

35. The coefficient of friction depends upon

A. area of contact only
B. nature of surface only
C. both (a) and (b)
D. none of these

Correct Answer: B. nature of surface only

36. The kinetic energy of a body __________ upon its mass and velocity.

A. does not depend
B. depends

37. According to Newton’s first law of motion,

A. every body continues in its state of rest or of uniform motion, in a straight line, unless it is acted upon by some external force
B. the rate of change of momentum is directly proportional to the impressed force, and takes place in the same direction, in which the force acts
C. to every action, there is always an equal and opposite reaction
D. none of the above

Correct Answer: A. every body continues in its state of rest or of uniform motion, in a straight line, unless it is acted upon by some external force

38. The moment of inertia of a square of side (a) about an axis through its center of gravity is

A. a4/4
B. a4/8
C. a4/12
D. a4/36

39. The velocity ratio of a single purchase crab winch can be increased by

A. increasing the length of the handle