# Engineering Mechanics – Section 6

21. The cartesian equation of trajectory is(where u = Velocity of projection, α = Angle of projection, and xy = Co-ordinates of any point on the trajectory after t seconds.)

A. y = (gx²/2u² cos²α) + x. tanα
B. y = (gx²/2u² cos²α) – x. tanα
C. y = x. tanα – (gx²/2u² cos²α)
D. y = x. tanα + (gx²/2u² cos²α)

Correct Answer: C. y = x. tanα – (gx²/2u² cos²α)

22. In collision of elastic bodies, the coefficient of restitution is the ratio of the relative velocity after impact to the relative velocity before impact.

A. True
B. False

23. In a framed structure, as shown in the below figure, the forces in the members AB and BC are respectively

A. √3. W (tensile) and 2W (compressive)
B. 2W (tensile) and √3. W (compressive)
C. 2√3. W (tensile) and 2√3. W (compressive)
D. None of the above

Correct Answer: A. √3. W (tensile) and 2W (compressive)

24. The acceleration of a particle moving with simple harmonic motion is proportional to the displacement of the particle from the mean position.

A. True
B. False

Correct Answer: A. True

25. The unit of moment of inertia of an area is

A. kg-m2
B. kg-m-s2
C. kg/m2
D. m4

Correct Answer: D. m4

26. The moment of inertia of a thin rod of mass m and length l, about an axis through its center of gravity and perpendicular to its length is

A. ml2/4
B. ml2/ 6
C. ml2/8
D. ml2/12

Correct Answer: D. ml2/12

27. When a body of mass m attains a velocity v from rest in time t, then the kinetic energy of translation is

A. mv2
B. mgv2
C. 0.5 mv2
D. 0.5 mgv2

Correct Answer: C. 0.5 mv2

28. The unit of angular velocity is

A. m/min
C. revolutions/min
D. both (B) and (C)
E. none of these

Correct Answer: D. both (B) and (C)

29. If a number of forces are acting at a point, their resultant is given by

Correct Answer: Option B

30.  A force acting in the opposite direction to the motion of the body is called force of friction.

A. Agree
B. Disagree

Correct Answer: A. Agree