Q.7
Which one of the following lists has the quantities force, kinetic energy and momentum correctly identified as scalar or vector?
| force | kinetic energy | momentum | |
| A | scalar | scalar | scalar |
| B | scalar | vector | vector |
| C | vector | scalar | scalar |
| D | vector | scalar | vector |
Answer: D
Force and momentum are vector quantities.
Kinetik energy is a scalar quantity.
Q.8
Fig. 1 shows the directions and lines of action of two forces applied to a circular disc.
Which one of the arrows in Fig. 2 best represents the line of action of the resultant force?
Answer: C
The line of action of the resultant force shoud originate from the intersection of the lines of action of the 2 forces.
Q.9
The given diagram shows the directions of three co-planar force, of magnitudes 20 N, 40 N and 50 N, applied to a particle at P.
What is the approximate bearing of the additional force required to maintain equilibrium?
A 370
C 1430
Answer: D
Sketch vector diagram of forces:
For equilibrium, the vector representing the additional force A must end at P.
Q.10
Two forces of magnitudes 4 N and 6 N are applied to a point.
Which one of the following could not be the magnitude of their resultant?
A 1 N B 4 N C 8 N D 10 N
Answer: A
The magnitude of the resultant is maximum (10 N) when the forces are in the same direction, and minimum (2 N) when the force are in the opposite directions.
So, the magnitude of the resultant ranges from 2 N to 10 N.
Q.11
The given diagram shows a particle with an initial velocity of 15 m s-1 in the Ox direction. Its velocity, at a later time, is 15 m s-1 at an angle of 600 to Ox. (Directions are given as angles measured anticlockwise from the direction Ox.)
What change of velocity has taken place in this interval?
A zero
B 26 m s-1 at an angle of 300 to Ox.
C 15 m s-1 at an angle of 1200 to Ox
D 15 m s-1 at an angle of 3600 to Ox
Answer: C
vchange = vfinal – vinitial (in the usual notations)
Sketch vector diagram of velocities:
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