Mechanical Engineering Principles

38 MECHANICAL ENGINEERING PRINCIPLES

3. Which of the following is not a vector
   quantity?

(a) displacement (b) density

(c) velocity (d) acceleration

4. Which of the following statements is
   false?

(a) Scalar quantities have size or mag-

nitude only

(b) Vector quantities have both magni-

tude and direction

(c) Mass, length and time are all scalar

quantities

(d) Distance, velocity and acceleration

are all vector quantities

5. If the centre of gravity of an object
   which is slightly disturbed is raised and
   the object returns to its original position
   when the disturbing force is removed,
   the object is said to be in

(a) neutral equilibrium

(b) stable equilibrium

(c) static equilibrium

(d) unstable equilibrium

6. Which of the following statements is
   false?

(a) The centre of gravity of a lamina is

at its point of balance.

(b) The centre of gravity of a circular

lamina is at its centre.

(c) The centre of gravity of a rectangu-

lar lamina is at the point of inter-

section of its two sides.

(d) The centre of gravity of a thin uni-

form rod is halfway along the rod.

7. The magnitude of the resultant of the
   vectors shown in Figure 3.29 is:

5 N

7 N

Figure 3.29

(a)2N (b)12N

(c) 35 N (d)−2N

8. The magnitude of the resultant of the
   vectors shown in Figure 3.30 is:

(a) 7 N (b) 5 N (c) 1 N (d) 12 N

4 N

3 N

Figure 3.30

9. Which of the following statements is
   false?

(a) There is always a resultant vector

required to close a vector diagram

representing a system of coplanar

forces acting at a point, which are

not in equilibrium.

(b) A vector quantity has both magni-

tude and direction.

(c) A vector diagram representing a

system of coplanar forces acting at

a point when in equilibrium does

not close.

(d) Concurrent forces are those which

act at the same time at the same

point.

10. Which of the following statements is
    false?

(a) The resultant of coplanar forces of

1 N, 2 N and 3 N acting at a point

can be 4 N.

(b) The resultant of forces of 6 N and

3 N acting in the same line of

action but opposite in sense is 3 N.

(c) The resultant of forces of 6 N and

3 N acting in the same sense and

having the same line of action is

9N.

(d) The resultant of coplanar forces of

4Nat0°,3Nat90° and 8 N at

180 °is 15 N.