Linear Momentum unit test
A test on this unit alone, marked as a percentage and a letter grade — for the test your class is actually sitting, rather than for May. Answer everything, then submit once: seeing the answer to question 3 before attempting question 4 makes the final percentage meaningless.
Perfectly inelastic collision
Impulse-momentum theorem
Equal speeds, different momenta
Why airbags work
Recombining component momenta
Why momentum is conserved in collisions
Impulse and momentum share units
Momentum in a system with external forces
The condition for momentum conservation
K = p²/2m
Impulse from a force–time graph
Identifying whether momentum is conserved
Short answer 1. Define or explain: Perfectly inelastic collision speed
3 ptsShort answer 2. Define or explain: Center-of-mass velocity
3 ptsShort answer 3. Define or explain: Momentum is a vector
3 ptsShort answer 4. Define or explain: Momentum vs kinetic energy
3 ptsFree response
12 ptsTRANSLATION BETWEEN REPRESENTATIONS (Question 2, 12 points). Two small disks are on a straight horizontal track with negligible friction. At t = 0, Disk R (mass m0) is at x = 0 moving with speed v0 in the +x-direction; Disk S (mass 3m0) is at rest ahead of it (Figure 1, top view). At t = t1 the disks collide; immediately afterward Disk R moves with speed v0/2 in the −x-direction. Figure 2 (given) is a momentum-vector diagram before the collision: an arrow of magnitude m0v0 pointing in +x for Disk R, and "p = 0" for Disk S. Figure 3 provides dots for drawing the after-collision momentum vectors. Figure 4 (given) graphs position x versus time t from 0 to t1: Disk R rising with slope v0 from the origin, Disk S a horizontal line at its initial position, and the center of mass rising with slope v0/4.
A. Describe the momentum arrows for Disk R and Disk S after the collision (Figure 3): direction of each arrow and length relative to the before-collision scale (write "p = 0" if a momentum is zero).
B. Starting with conservation of linear momentum, derive an expression for the kinetic energy of Disk S immediately after the collision, in terms of m0, v0, and physical constants, as appropriate.
C. Describe the three lines on the Figure 4 graph representing the positions x of Disk R, Disk S, and the center of mass of the two-disk system from t = t1 to t = 2t1, distinctly labeled.
D. During the collision the magnitudes of the momentum changes of Disks R and S are ΔpR and ΔpS. Indicate whether ΔpR is greater than, less than, or equal to ΔpS, and briefly justify by referencing a fundamental physics principle.