What Formula to Use for Elevator's Constant Acceleration Problem?

[mb85]

hello. i am confused on what formula in particular you use to figure the answer out?

A certain elevator cab has a total run of 209 m and a maximum speed is 322 m/min, and it accelerates from rest and then back to rest at 1.16 m/s2. (a) How far does the cab move while accelerating to full speed from rest? (b) How long does it take to make the nonstop 209 m run, starting and ending at rest?

 

[StatusX]

Assuming the acceleration is constant, you can use a=∆v/∆t, and then x=1/2at². For the second part, you'll need to separate into three phases: acceleration, constant velocity, and decceleration. Find the time each part takes. Also, remember to use the consistent units.

 

[mb85]

im still confused.. and am not getting the correct answer on egrade. :(

 

[andrewchang]

there's three separate parts:
1. the car is accelerating to its top speed
2. the car is moving at its top speed
3. the car is decelerating to rest

for part A, you just need to use kinematics. you are given enough information to use the equations and get the answer.

for part B, you need to use the three parts. find the distance that the car travels at the max velocity, and get the time. you can add this time to the time it takes to accelerate and decelerate.