53kg girl weights by standing on a scale in an elevator What

53kg girl weights by standing on a scale in an elevator. What does the scale read when: The elevator is descending at a constant rate of 12 m/s^? The elevator is accelerating downward at 1.1 m/s^2? The levanter is accelerating upward at 1.1 m/s^2? The elevator is ascending at 12 m/s but its speed is decreasing by 2 m/s in each second?

Solution

A. In this case the only acceleration is gravity

So reading will be

F = mg = 53*9.81 = 519.93 N

B. Elevator accelerate down so girl feels less weight on her feet

F = mg - ma = 519.93 - 53*1.1 = 461.63N

C. Elevator accelerate up so girl feels more weight on her feet

F = mg + ma = 519.93 + 53*1.1 = 578.23 N

D. \"ascending\" and \"speed decreasing\" means that the direction of acceleration is downward

acceleration = 2 m/s per sec = 2 m/sec^2

F = 519.93 - 53*2 = 413.93 N