Tina and her puppy are tugging on a rope, each pulling on opposite ends. When is Tina doing work?

Work is done when a force causes an object to move in the direction of that force. When Tina pulls the puppy toward her, the rope and puppy move in the direction of her pull, so she does work. Holding the rope steady causes no movement, and after she lets go she is no longer exerting a force.

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