PHYSICS · Multi-part · AP · Physics 1: Algebra-based · Linear Momentum · Linear Momentum
Problem
Two low-friction gliders, A and B, move toward one another on a straight horizontal air track. A is to the left of B. Initially you choose the conventional coordinate system in which the +x-axis points to the right.
• Glider A: mass mA=0.40kg, velocity +0.80ms−1
• Glider B: mass mB=0.60kg, velocity −0.50ms−1 (the minus sign is based on your initial axis choice)
The gliders collide and stick together.
Immediately after the collision a lab partner re-defines the axis so that the +x-direction now points to the left (opposite your original choice). No other quantities are re-measured.
Answer the following, using clear verbal reasoning in addition to any calculations.
(a) Calculate the numerical value (with sign) of the initial momentum of the two-glider system using the original axis definition.
(b) Determine the magnitude and direction (expressed as a signed number) of the velocity of the stuck-together gliders immediately after the collision, still using the original axis.
(c) Translate your answers from parts (a) and (b) into the new coordinate system adopted after the collision. Show how each sign changes or stays the same.
(d) Explain, without further calculation, why any observer—regardless of axis choice—must agree on the physical speed and direction of motion of the joined gliders even though the numerical signs in (b) and (c) differ.