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.
When to use energy instead of forces
Conservative vs non-conservative forces
A watt is a joule per second
Work done by friction
Power in terms of velocity
Thermal energy from friction uses path length
Internal (thermal) energy
Energy in a spring launcher
Work from a graph
Energy in a pendulum
Why mass cancels in energy problems
Choosing energy or kinematics
Short answer 1. Define or explain: Conservation of mechanical energy
3 ptsShort answer 2. Define or explain: Conservation of mechanical energy condition
3 ptsShort answer 3. Define or explain: Hooke's law
3 ptsShort answer 4. Define or explain: Why friction has no potential energy
3 ptsFree response
12 ptsA spring of spring constant k is compressed a distance d by a cart of mass m and then released. The cart leaves the spring at the bottom of a frictionless incline that makes an angle θ with the horizontal, travels up the incline, and momentarily comes to rest at a maximum distance D along the incline surface. Figure 1 (given) is an energy bar chart for the instant the spring is fully compressed and the cart is at rest, on a scale where each division is E₀: the spring potential energy Us is 8E₀ and the kinetic energy K and gravitational potential energy Ug are both zero. Gravitational potential energy is defined to be zero at the bottom of the incline.
A. Describe the energy bar charts for two later instants on the same E₀ scale: (i) the moment the cart loses contact with the spring at the bottom of the incline, and (ii) the moment the cart is momentarily at rest at its highest point on the incline.
B. Starting from conservation of energy, derive an expression for the maximum distance D traveled along the incline, in terms of k, d, m, θ and physical constants.
C. Describe the graph of the cart’s kinetic energy K as a function of distance s traveled along the incline, from s = 0 to s = D, including its intercepts and shape.
D. The experiment is repeated with the incline angle increased while everything else is unchanged. Indicate whether the maximum distance along the incline increases, decreases, or stays the same, and justify your answer.