(adsbygoogle = window.adsbygoogle || []).push({}); 1. The problem statement, all variables and given/known data

You are moving into an apartment and take the elevator to the 6th floor. Does the force exerted on you by the elevator do positive or negative work when the elevator (a) goes up and (b) goes down? Explain your answers.

Suppose your weight is 685N and that of your belongings is 915N. (a) Determine the work done by the elevator in lifting you and your belongings up to the 6th floor (15.2m) at a constant velocity. (b) How much work does the elevator do on you alone (without belongings) on the downward trip, which is also made at a constant velocity?

2. Relevant equations

W=Fdcos(theta)

3. The attempt at a solution

For the concept question, I know that work is negative when it is going in the opposite direction of the force, but I'm thrown off by which force. The question indicates that there is no acceleration, so there is a gravitational pull downwards equal to a normal force upwards. So which force is supposed to be opposed?

As for the second part, this is what I got:

685+915=1600N

1600(15.2)(cos0)=24320J

685(15.2)(cos180)=-10412J

BUT here's what confuses me - since displacement is a vector quantity, shouldn't one of the above equations have a negative displacement since it's going in the opposite direction?

Argh, I've been mulling over this and I'm still so confused. Please help!

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# Homework Help: Positive vs. negative work in an elevator?

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