Time it takes to lift a sofa with power

  • Thread starter Thread starter Capncanada
  • Start date Start date
  • Tags Tags
    Lift Power Time
Click For Summary

Homework Help Overview

The problem involves lifting a sofa using a motor, focusing on the time required for the lift given the motor's power and the sofa's weight and height. The subject area includes concepts from mechanics, specifically energy conservation and power.

Discussion Character

  • Exploratory, Conceptual clarification, Mathematical reasoning

Approaches and Questions Raised

  • Participants discuss the application of conservation of energy, questioning how kinetic and potential energy relate in the context of lifting the sofa. There are attempts to connect power, work, and time in the context of the problem.

Discussion Status

The discussion has explored various interpretations of energy conservation and the relationship between power and time. Some participants have provided guidance on understanding the relevant equations and units, while others are clarifying the role of kinetic and potential energy in the scenario.

Contextual Notes

Participants are navigating through the implications of lifting the sofa at a constant speed and the associated energy transformations. There is an emphasis on understanding units and the definitions of work and power in the context of the problem.

Capncanada
Messages
52
Reaction score
0

Homework Statement



Your sofa won't fit through the door of your new sixth-floor apartment, so you use a 1.18 kW motor to lift the 84.7 kg sofa 18.8 m from the street.

How much time does the lift take?

Homework Equations



KE_i+PE_i=KE_f+PE_f
(If forces are conserved? I'm not sure if so.)

The Attempt at a Solution



KE_i=PE_f
1/2mv^2=mgh
1/2v^2=gh
This leads to a dead end I think, velocity ends up being very large..
 
Physics news on Phys.org
Presumably, the sofa is lifted at a constant speed, so its kinetic energy doesn't change.
 
So conservation of energy would apply, so the Kinetic energy will equal the potential energy of the sofa at the top?

With the conservation equation how would I get to the units of time?
 
I repeat, the Kinetic Energy doesn't change. It remains the same.

What is power?
 
Power is work over time.
 
If the work doesn't go into increasing the K.E., then What form of energy is being increased as the piano is lifted?
 
The potential energy increases..
 
Right.

So how much energy must the sofa gain to make it to the 6th floor?
 
Found it, I need to gain a better grasp for what my units are. Thank you for getting me started on it. I found the PE=mgh and that is the work done.

t=w/p gets me my answer.
 
  • #10
Yup. That's it.
 

Similar threads

  • · Replies 2 ·
Replies
2
Views
8K
  • · Replies 14 ·
Replies
14
Views
6K
  • · Replies 3 ·
Replies
3
Views
4K
Replies
7
Views
2K
  • · Replies 7 ·
Replies
7
Views
3K
  • · Replies 1 ·
Replies
1
Views
3K
  • · Replies 3 ·
Replies
3
Views
3K
  • · Replies 4 ·
Replies
4
Views
21K
  • · Replies 19 ·
Replies
19
Views
4K
Replies
2
Views
5K