Unit EM Extension F Quiz
Consider the case of the hockey player and the puck, but this time consider what happens while the player is using his muscles to swing his hockey stick before it hits the puck. Evaluate the following explanation for why the hockey stick speeds up as it gets closer to the puck. (You should draw your own G/R energy diagram on a separate sheet before reading the explanation.) (1) As the player swings the hockey stick towards the puck, there is a contact push/pull interaction between the player and the stick. (2) During this interaction, energy is transferred from the hockey player to the stick, the player decreases his chemical potential energy, and the kinetic energy of the hockey stick increases. (3) Because the kinetic energy increases, the hockey stick speeds up as it gets closer to the puck. This explanation is
A. Accurate as written.
A previous student wrote the following explanation for how 'brake fade' occurs. Evaluate this explanation for accuracy. (1) When the brake pedal is pushed down, there is a friction-type contact push/pull interaction between the brake pads and the wheels. (2) As a result, energy is transferred from brake pads to the wheels. (3) The thermal energy of the brake pads increases. (4) The kinetic energy of the wheels decreases and their thermal energy increases. (5) As the thermal energy of the brake pads increase, they get very hot and the pad surface wears out; this is what causes 'brake fade.' This explanation is
C. Inaccurate because sentence #2 is incorrect.
When you apply the brakes on a bicycle, pads of rubber are pushed against the metal rims of the wheels to slow them down via a friction-type contact push/pull interaction between them. One of the problems that can occur with bicycle brakes is that of 'brake fade', which is the loss of the brakes' ability to stop the bicycle. (This usually happens with prolonged heavy use of the brakes, such as when descending a steep hill.) Which of the following G/R energy diagrams best describes the interaction between the brake pads and the wheels? Hint: When answering this question, consider only the energy transfer. What object(s) loses energy (overall), the wheel or the brake pads? What gains energy? What does that imply about the direction of the energy transfer arrow?
Energy Diagram D
