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.

Here is important to choose a reference frame, we are going to use positive direction downward, so after pushing the button the elevator is moving downward before it stops so the sign of the velocity is positive. If we assume the force the brakes apply on the elevator to stop it is constant, then the acceleration is constant to because Newton's second law. For constant acceleration, acceleration can be defined as the change of velocity over time:

[tex]\overrightarrow{a}=\frac{\overrightarrow{V_final}-\overrightarrow{V_initial}}{t} [/tex]

The final velocity is zero because the elevator stops, so:

[tex]\overrightarrow{a}=\frac{-\overrightarrow{V_initial}}{t} [/tex]

Because in our reference frame the initial velocity of the elevator is positive and time is always positive, then the acceleration is negative IN OUR REFRENCE FRAME.

funmilaciousfunmie78 funmilaciousfunmie78 · Answer 2 · 2020-02-13T05:03:08+01:00

Answer:

velocity and acceleration have these signs respectively (- , +)

Explanation:

The The equation below shows the relationship between the velocity and acceleration of and object :

a⃗=dv/dt

Acceleration is the rate of change of velocity with time.

There is a decrease in velocity i with time such that the rate is negative. This results into the deceleration which acts to slow down any motion in the direction of motion.

Therefore, the acceleration direction is opposite to the direction of deacceleration such that the direction of acceleration is upwards.