@ould the elevator be moving up or down?

[elizabethR]

elevator ??

A 615 N student standing on a scale in an elevator notices that the scale reads 645 N. would the elevator be moving up or down?

 

[neutrino]

What do you think is the answer (and why)?

 

[elizabethR]

well i think that he would be moving down because the scale says he got heavier. i think that the force pushing down would make him seem heavier

 

[neutrino]

Double post

 

[neutrino]

Not so. The elevator must either be accelerating up or down for his scale to show a different reading. The reading is nothing but the force the scale exerts on the person to keep him in place with respect to the elevator. Let's assume that the elevator is accelaratig down, then you can easily show from a free body diagram that the scale reading must decrease. Therefore he is accelerating up.