Physics quiz question: energy changes of a dragged box speeding up a ramp

Physics 205A Quiz 5, fall semester 2018
Cuesta College, San Luis Obispo, CA

A Physics 205A student pulls a 15.0 kg box with increasing speed up a ramp with a rope that is parallel to the slope of the ramp. Friction is not negligible. Ignore drag. For this process, the __________ of the box increases.
(A) gravitational potential energy.
(B) translational kinetic energy.
(C) (Both of the above choices.)
(D) (Neither of the above choices.)

Correct answer (highlight to unhide): (C)

The change in translational kinetic energy is given by:

∆KE_tr = (1/2)·m·(v_f² – v₀²).

Since the speed of the box is increasing, v_f is faster than v₀, and so KE_tr is increasing (∆KE_tr is positive).

The change in gravitational potential energy is given by:

∆PE_grav = m·g·(y_f – y₀).

Since y_f is higher than y₀, then PE_grav also increases (∆PE_grav is positive).

Sections 70854, 70855
Exam code: quiz04JuR4
(A) : 17 students
(B) : 7 students
(C) : 28 students
(D) : 0 students

Success level: 54%
Discrimination index (Aubrecht & Aubrecht, 1983): 0.75