Vectors & Scalars Questions and Answers 1

 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 127⁰

C 143⁰                                D 217⁰

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

v_change = v_final – v_initial (in the usual notations)

Sketch vector diagram of velocities: