Question

5-3 now the elevator and the girl standing on the scale are mid - floor and are moving at a constant speed upward. which choice properly describes her weight, contact force, and acceleration at this point?
○a. weight = 130 lbs downward, contact force = 130 lbs upward, acceleration is zero
○b. weight = 130 lbs downward, contact force = 130 lbs upward, acceleration is downward
○c. weight = 130 lbs downward, contact force = 130 lbs upward, acceleration is upward
○d. weight = 140 lbs downward, contact force = 130 lbs upward, acceleration is downward
○e. weight = 140 lbs downward, contact force = 130 lbs upward, acceleration is upward
○f. weight = 130 lbs downward, contact force = 140 lbs upward, acceleration is upward
○g. weight = 130 lbs downward, contact force = 140 lbs upward, acceleration is downward
5-4 as the elevator approaches the second floor, it begins to slow to a stop. which choice prop

Explanation:

Step1: Analyze the motion

The elevator is moving at a constant speed. According to Newton's first - law, an object moving at a constant speed has zero acceleration since there is no change in velocity ($a = 0$).

Step2: Analyze the forces

The girl's weight ($W$) acts downward. The contact force ($N$) from the scale on the girl acts upward. According to Newton's second - law $F_{net}=ma$. Since $a = 0$, the net force $F_{net}=N - W=0$, so $N = W$. Given the weight is 130 lbs downward, the contact force is 130 lbs upward.

Answer:

A. weight = 130 lbs downward, contact force = 130 lbs upward, acceleration is zero