# Elevator with constant acceleration

## Homework Statement

The Stratosphere Tower in Las Vegas is 1137 ft high. It takes 1 min, 20 s to ascend from the ground floor to the top of the tower using the high-speed elevator. The elevator starts and ends at rest. Assume that it maintains a constant upward acceleration until it reaches its maximum speed, and then maintains a constant acceleration of equal magnitude until it comes to a stop. Find the magnitude of the acceleration of the elevator.

The trip consists of two constant-acceleration segments, each of which has the same duration. You know the total displacement of the elevator.

h = v0t + 0.5at2

## The Attempt at a Solution

The last sentence makes me think the elevator accelerates to a certain speed, which it reaches half way up, and then decelerates with the same magnitude, stopping at the top.
Assume that it maintains a constant upward acceleration until it reaches its maximum speed, and then maintains a constant acceleration of equal magnitude until it comes to a stop

This would mean
h = 568.5 = 0 +0.5(a)(402
a = 0.71ft/sec

I can't think of another way to solve this, but that isn't the correct answer.

SammyS
Staff Emeritus
Homework Helper
Gold Member

## Homework Statement

The Stratosphere Tower in Las Vegas is 1137 ft high. It takes 1 min, 20 s to ascend from the ground floor to the top of the tower using the high-speed elevator. The elevator starts and ends at rest. Assume that it maintains a constant upward acceleration until it reaches its maximum speed, and then maintains a constant acceleration of equal magnitude until it comes to a stop. Find the magnitude of the acceleration of the elevator.

The trip consists of two constant-acceleration segments, each of which has the same duration. You know the total displacement of the elevator.

h = v0t + 0.5at2

## The Attempt at a Solution

The last sentence makes me think the elevator accelerates to a certain speed, which it reaches half way up, and then decelerates with the same magnitude, stopping at the top.

This would mean
h = 568.5 = 0 +0.5(a)(402
a = 0.71ft/sec

I can't think of another way to solve this, but that isn't the correct answer.
For one thing, you units of acceleration are incorrect.

ft/sec^2....I forgot to type the 2

PhanthomJay
Homework Helper
Gold Member
it could be a significant figure thing....a = 0.7 ft/sec^2...or perhaps a 'book' error

it could be a significant figure thing....a = 0.7 ft/sec^2...or perhaps a 'book' error
Ok good, so you agree that I'm reading the problem correctly?

PhanthomJay