Bridge in the Context of A Spring.

[las2vc]

We have weekly problem sets that lead us through a "story" of sorts. In this week's, a group of tourists are on a newly-built, albeit poorly-designed bridge. The question reads:

"The tourists bend their knees and, at the count of three, jump upward simultaneously. While their feet are in contact with the bridge, as they straighten out their legs during their jump, are the tourists in equilibrium? Why or why not?"

I know that equilibrium means to have a constant velocity. I was thinking that they WERE in equilibrium because even though they're accelerating upward (?), they're not moving and therefore their velocity is constant at zero until their feet leave the bridge. Does this make sense? Is that appropriate physics 'language'? It seems that I'm missing some key terminology or something that would make it sound more articulate.

Thanks!
Laura.

 

[member 553083]

Yes, your reasoning is correct. The tourists are in equilibrium while their feet are in contact with the bridge, since they are not moving. You could say that the tourists are at rest and maintain a state of static equilibrium as they jump.