Unit 4 Activity 2 Extension B Quiz

This question again refers to the demonstration you previously saw that was referred to in the last question. Assuming the speed of the cart is indeed constant, which one of these force diagrams is the most appropriate for the cart just after the initial push?

A.

Previously, you saw a demonstration (or a movie of one) involving a cart that had two fan units pushing on it in opposite directions with equal strength. With the cart initially at rest, it was given a push to start it moving. Here is the force diagram for that cart when: Which one of these force diagrams is the most appropriate for the cart at a moment during the short period it is getting the push that starts it moving?

C.

After completing the first part of this homework assignment, Luisa made this comment:

C. ) Another push is needed to start such an object moving, and during that push, the forces are unbalanced.

After a hockey player gives a puck a quick 'hit' with his stick, the puck slides across the ice at a speed that is essentially constant. A student in a previous class offered the following force diagram and explanation for why the speed of the puck is constant after the hit. "The initial hit exerts a force on the puck, making the forces acting on the puck unbalanced, and so it starts to move. After the hit ends there is no net force acting on the puck, and when the net force acting on an object is zero, its speed does not change. So after the stick has lost contact with the puck, its speed remains constant." What is your evaluation of this explanation?

C. The force diagram is problematic but the narrative is accurate.