A passenger standing in a city bus experiences a backward jerk when the bus suddenly…
PHYSICS · Multi-part · AP · Physics C: Mechanics · Force and Translational Dynamics · Force and Translational Dynamics
Problem
A passenger standing in a city bus experiences a backward jerk when the bus suddenly starts moving forward from rest. Two observers watch the event—one standing on the road and the other standing inside the bus.
(a) Explain, using Newton’s first law of motion, why the passenger appears to jerk backward as seen by the observer on the road.
(b) State, with reason, whether the interior of the bus can be regarded as an inertial frame at the instant the bus starts moving.
(c) The observer inside the bus draws a free-body diagram of the passenger and wishes to apply Newton’s second law in its usual form. Identify the additional force that must be included and specify its qualitative direction relative to the motion of the bus.