posted by help .
A 70kg man stands on a bathroom scale in an elevator. As the elevator starts moving, the scale reads 90kg
Is the elevator acceleration up or down, is the elevator moving up or down?
i think you mean it's weight (units in N), because mass is constant.
anyway, since the weight increased, the elevator accelerates and moves up. :)
Force up on man - weight of man = m a up
F scale - m g = m a
Fscale = 90*9.8
90*9.8 - 70*9.8 = 70 a
a = 20*9.8 /70
the acceleration is up
since we started from rest, we will be moving up but have not gained any speed yet