For each of the motions described below, determine the algebraic sign (+, -, or 0) of the velocity and acceleration of the objec

Question

13 days ago

14

For each of the motions described below, determine the algebraic sign (+, -, or 0) of the velocity and acceleration of the objec

t at the time specified. For all of the motions, the positive y axis is upward.
Part A
An elevator is moving downward when someone presses the emergency stop button. The elevator comes to rest a short time later. Give the signs for the velocity and the acceleration of the elevator after the button has been pressed but before the elevator has stopped.
Enter the correct sign for the elevator's velocity and the correct sign for the elevator's acceleration, separated by a comma. For example, if you think that the velocity is positive and the acceleration is negative, then you would enter +,- . If you think that both are zero, then you would enter 0,0 .

Part B
A child throws a baseball directly upward. What are the signs of the velocity and acceleration of the ball immediately after the ball leaves the child's hand?
Enter the correct sign for the baseball's velocity and the correct sign for the baseball's acceleration, separated by a comma. For example, if you think that the velocity is positive and the acceleration is negative, then you would enter +,- . If you think that both are zero, then you would enter 0,0 .

Part C
A child throws a baseball directly upward. What are the signs of the velocity and acceleration of the ball at the very top of the ball's motion (i.e., the point of maximum height)?
Enter the correct sign for the baseball's velocity and the correct sign for the baseball's acceleration, separated by a comma. For example, if you think that the velocity is positive and the acceleration is negative, then you would enter +,- . If you think that both are zero, then you would enter 0,0 .

Physics

1 answer:

serg [1.1K] · Answer 1 · 2026-02-20T18:39:19+03:00

Part A: -,+

The elevator descends, dictating the velocity's direction, which aligns with the movement's path. With the positive direction defined as upward, the velocity is negative. After the emergency button is pressed, the elevator begins to stop, indicating that the velocity is decreasing. Therefore, the acceleration is oriented in the opposite way to the velocity, making its sign +.

Part B: +, -

The ball ascends, which determines the positive direction of the velocity. Hence, the velocity is positive.

Once the ball is thrown, the only force acting on it is gravity, opposing the ball’s ascent and causing it to descend. This means the acceleration is directed downwards, resulting in a negative sign.

Part C: 0, -

Throughout the ball's trajectory from the moment it's thrown until it drops to the ground, gravity constantly exerts downward acceleration (-).

After the throw, the ball's velocity will decline due to gravity. When it reaches a velocity of 0, it achieves its peak height. At this specific moment, the ball begins to descend again under the influence of gravity. However, at the peak height, the ball's velocity is 0.