Question

(ii) a woman stands on a bathroom scale in a motionless elevator. when the elevator begins to move, the scale briefly reads only 0.75 of her regular weight. calculate the acceleration of the elevator, and find the direction of acceleration.

Answer 1

2.45 m/s^2 Elevator is moving down. The woman's weight is a function of the local gravity plus the local acceleration, an expression for this would be G + A = 0.75 G = Normal attraction due to gravity A = Weight due to acceleration. Substituting 1 for G gives 1 + A = 0.75 Solving for A 1 + A = 0.75 A = -0.25 So the acceleration experienced is -0.25 times the acceleration due to gravity. So multiply by 9.8 m/s^2 -0.25 * 9.8 m/s^2 = -2.45 m/s^2 So the woman briefly experienced an acceleration of 2.45 m/s^2 as the elevator started moving. And since her weight decreased, that means that the elevator started moving down.