posted by james .
A shoe case weighing 40 lb is located on a scale inside a moving elevator that is going upward with the speed of 8 m/s. At time T1 elevator slows down with the acceleration of 3 m/s2 until the time T2. What are the the readings of the scale at T2 and T1 respectively?
While the upward velocity is decreasing, there is downward acceleration at rate a = 3 m/s^2
At time T1, the scale reads force F.
W - F = M a
F = W - M a = W - (W/g) a
= W (1 - a/g) = 40 lb * (6.8/9.8)
If acceleration = 0 at T2, the scale reads 40 lb then. We are able to use metric units for a and g because We are calculating a ratio.