Teaching Physics with the Physics Suite Edward F. Redish

Pushing a box

A worker is pushing a cart along the floor. At first, the worker has to push hard in order to get the cart moving. After a while, it is easier to push. Finally, the worker has to pull back on the cart in order to bring it to a stop before it hits the wall. The force exerted by the worker on the cart is purely horizontal. Take the direction the worker is going as positive.

Below at the right are shown graphs of some of the physical variables of the problem. Match the graphs with the variables in the list at the left below. You may use a graph more than once or not at all. (Note: the time axes are to the same scale, but the ordinates {"y axes"} are not.)

 friction force force exerted by the worker net force acceleration velocity

Note to the instructor: This problem can be made more challenging (and revealing) by having the students draw the graphs themselves instead of selecting them from a given set.

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