Work, Energy, and Power 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.
Nonconservative work
Potential energy curves
Energy bar charts
Work as a dot product
Second derivative test for stability
Zero work from perpendicular forces
Escape energy
Spring potential energy
Conservative forces and path independence
Deriving force from U(x)
Power delivered by a constant force
Power as the rate of doing work
Short answer 1. Define or explain: Escape speed is mass independent
3 ptsShort answer 2. Define or explain: Instantaneous power as force dotted with velocity
3 ptsShort answer 3. Define or explain: Total energy of an elliptical orbit
3 ptsShort answer 4. Define or explain: Instantaneous power
3 ptsFree response
10 ptsStudents investigate the coefficient of kinetic friction between a block and a horizontal surface. They give the block an initial speed v₀ and measure the distance d it slides before coming to rest. They repeat the experiment for several initial speeds. v₀ (m/s) 1.0 1.5 2.0 2.5 3.0 d (m) 0.15 0.33 0.60 0.92 1.32
A(i). Describe a procedure the students could use to give the block a measurable, repeatable initial speed. A(ii). Describe one step that would reduce experimental uncertainty.
B(i). Derive an expression relating the sliding distance d to the initial speed v₀ and the coefficient of kinetic friction μ_k. B(ii). Indicate what quantities the students should graph to obtain a straight line usable to determine μ_k.
C(i). Calculate the values to be plotted on the horizontal axis. C(ii). Describe the axis labels, with units, the positions of the plotted points, and the best-fit line.
D. Using the best-fit line described in part C, calculate an experimental value for the coefficient of kinetic friction.