Question

In which direction does the accelerating force acts?

(a) Opposite to the motion

(b) Along the motion

(c) Perpendicular to motion

(d) Variable

I have been asked this question in an international level competition.

The question is from Frequency of Free Damped Vibrations in section Longitudinal and Transverse Vibrations of Machine Dynamics

Answer 1

Correct choice is (b) Along the motion

The explanation is: It is assumed that the frictional resistance to the motion of the body is directly proportional to the speed, therefore accelerating force on the mass acts in same direction to the motion of the mass.