Elevator with constant acceleration

[cowmoo32]

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.

Homework Equations

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]

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.

Homework Equations

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.

 

[cowmoo32]

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

 

[PhanthomJay]

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

 

[cowmoo32]

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]

Ok good, so you agree that I'm reading the problem correctly?

yes.