Consider the following three reference frames:
(A) The ground beside a straight railway track.
(B) A railway coach moving along the track with a constant speed of 60kmh−1.
(C) Another coach on the same track that is just starting from rest with a uniform acceleration of 2ms−2 in the forward direction.
a. (a) Using Newton’s first law as the test, identify which of the frames (A), (B) and (C) are inertial. Give a brief justification for each choice.
b. (b) A box of mass 3kg is placed on the floor of the accelerating coach (frame C). Calculate the magnitude and direction of the additional force that an observer in frame C must consider so that the box can be treated as being in equilibrium.
c. (c) Determine the net external force acting on the same box as measured by the observer standing on the ground (frame A).