- #1

Iwanttolearnphysics

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- Homework Statement
- A 50kg woman does push-ups by applying a force to elevate her center of mass by 0.2m. Estimate the number of push ups that the woman must do in order to expend 300J of energy.

- Relevant Equations
- W = Fs

Hello, everyone. I'm not sure if I did this problem right because there's no answer key. I got this question from a high school introductory Physics book. But it's jaded and I accidentally poured coffee on it, so I can't take a picture of the question. I copied it word for word though.

This is what I did, please let me know if I did anything wrong.

This is what I did, please let me know if I did anything wrong.

- W = mas
- W = 50(-9.8)(0.2)
- W = 98 J
- 300 J/98 J =3.06
- So I think it will take approximately 3 push ups for her to use up 500J of energy.
- I'm unsure if this is correct. What happens as the distance between her and the ground decreases? Does she do positive work while moving towards the ground? Does she do negative work while being lifted by her arms?
- According to wikipedia, work is the energy transferred to or from an object via the application of force along a displacement. In its simplest form, it is often represented as the product of force and displacement.
- Energy is a scalar quantity, but there is such a thing as negative work, right?
- If the work done while she's pushing up on the ground is negative, and the work done as she's coming back to the ground is positive, won't that mean that ultimately she didn't get any work done because they'll cancel out?

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