# How Much Power Does an Elevator Motor Need to Overcome Friction?

• gansta344u
In summary: No problem. You should start by drawing a free-body diagram. That will help you see how the various forces are acting on the object.
gansta344u
A 2.8e3 kg elevator carries a maximum load of 768.1 kg . A constant frictional force of 2.1e3 N retards the elevators motion upward. The acceleration of gravity is 9.81m/s^2. what is the minimum power must the motor deliver to lift the fully loaded elevator at a constant speed of 3.85m/s. answer in units of kW. please i need help on the question. if possible i need both the answer and a clear method on what was done to solve the problem

if u can i need help on a another problem.

a 35.0kg child is in a swing that is attached to ropes 2.20m long. The acceleration of gravity is 9.81m/s^2. Find the gravitational potential energy associated with the child relative to the lowest position when the ropes make a 31.0 degree angle with the vertical. awsner in units of J. please both method and answer would be appreciated

Well in the first sitaution you can use a pretty handy formula which says that

P=Fv

Here P is the "power" and F is the sum force acting on the body (in the direction of the movment). v stands for the velocity.

The tricky bit is to get F right. Forces opposing the movment is the totalt gravitational force and frictional force.

<< too much help given -- removed by berkeman >>

Last edited by a moderator:
gansta344u said:
A 2.8e3 kg elevator carries a maximum load of 768.1 kg . A constant frictional force of 2.1e3 N retards the elevators motion upward. The acceleration of gravity is 9.81m/s^2. what is the minimum power must the motor deliver to lift the fully loaded elevator at a constant speed of 3.85m/s. answer in units of kW. please i need help on the question. if possible i need both the answer and a clear method on what was done to solve the problem

if u can i need help on a another problem.

a 35.0kg child is in a swing that is attached to ropes 2.20m long. The acceleration of gravity is 9.81m/s^2. Find the gravitational potential energy associated with the child relative to the lowest position when the ropes make a 31.0 degree angle with the vertical. awsner in units of J. please both method and answer would be appreciated

You need to show us the relevant equations and your attempt at the solutions before we can offer any tutorial help. Please be sure to read the Homework Help rules at the "Rules" link at the top of the page.

Ofey said:
Well in the first sitaution you can use a pretty handy formula which says that

P=Fv

Here P is the "power" and F is the sum force acting on the body (in the direction of the movment). v stands for the velocity.

The tricky bit is to get F right. Forces opposing the movment is the totalt gravitational force and frictional force.

<< too much help given -- removed by berkeman >>

Welcome to the PF. This thread was originally misplaced in the general technical PF forums. It is clearly homework/coursework, though, so the Homework Help rules still apply, even before it is moved here to the HH forums. Please only offer tutorial help (not working out the problem for the OP), and only after the OP has shown some effort at working out the problem themselves. Thanks.

i have been trying it
what am i supposed to post the wrong answer too huh
am asking for help if u can then please otherwise i am not asking for the answer just the way and the formula if not please explain to me how am i supposed to show effort. i don't get that part

gansta344u said:
i have been trying it
what am i supposed to post the wrong answer too huh

Don't get snippy. You need our help, not the other way around. When you registered you were presented with the rules of Physics Forums, and you clicked "I Agree".

From the Rules:

Homework Help:
On posting questions: Any and all high school and undergraduate homework assignments or textbook style exercises for which you are seeking assistance are to be posted in the appropriate forum in our Homework & Coursework Questions area. This should be done whether or not the problem is part of one's coursework. The reason for this is that the scientific and mathematical sections of Physics Forums are to be reserved for discussions and not academic assistance. Since graduate level assignments are meant to be more thought provoking (and hence more worthy of discussion), graduate level questions will be allowed in the relevant part of the main section of PF, provided that the graduate student attempts the problem and shows his work. NOTE: You MUST show that you have attempted to answer your question in order to receive help. You MUST make use of the homework template, which automatically appears when a new topic is created in the homework help forums.

am asking for help if u can then please otherwise i am not asking for the answer just the way and the formula if not please explain to me how am i supposed to show effort. i don't get that part

You are supposed to type out what you've done for this problem. We can't possibly tell you what your error was if you don't show it to us.

ok I am just saying , i don't know your protocol so its OK if you do not want to help

gansta344u said:
ok I am just saying , i don't know your protocol so its OK if you do not want to help

Doing your homework for you is not going to be helping you to learn. Show us your attempt at solving the problems, and we can provide tutorial assistance. You will do the bulk of the work, as you should on your homework and coursework.

OK your probably right but for this problem i didnt know where to start. If i just knew what formula to use i could probably do the rest. I didnt really understand how to go about this problem so i just needed help in the basic concepts not the really the calculations.

gansta344u said:
OK your probably right but for this problem i didnt know where to start. If i just knew what formula to use i could probably do the rest. I didnt really understand how to go about this problem so i just needed help in the basic concepts not the really the calculations.

Power is force divided by time. P = F / t

The total force in the first question is the force to lift the elevator and to oppose the friction. Use the basic equation

F = ma

and figure out what all of the forces are on the elevator. Then you can use the time specified and the first equation to get much farther along toward the answer.

thanks for the help but it a little to late i already solved the problem but thanks anyways. sorry if i seemed in a bad mood just a little stressed and sorry I am new to the forum so i didnt know your protocol

gansta344u said:
thanks for the help but it a little to late i already solved the problem but thanks anyways. sorry if i seemed in a bad mood just a little stressed and sorry I am new to the forum so i didnt know your protocol

No worries. Glad you solved the problems. Get some sleep!

## What is power?

Power is the rate at which work is done or energy is transferred. It is measured in watts (W) and is calculated by dividing the amount of work done by the time it takes to do it.

## What is work?

Work is the application of force over a distance, resulting in the movement of an object. It is measured in joules (J) and is calculated by multiplying the force applied by the distance over which it is applied.

## What is the relationship between power and work?

The relationship between power and work is that power is the rate at which work is done. This means that the more powerful an object or person is, the more work they can do in a given amount of time. Conversely, the less powerful an object or person is, the less work they can do in a given amount of time.

## How can power and work be calculated?

Power can be calculated by dividing the amount of work done by the time it takes to do it. Work can be calculated by multiplying the force applied by the distance over which it is applied.

## What are some real-life examples of power and work?

Some real-life examples of power and work include lifting weights at the gym (applying force over a distance), a car accelerating (transferring energy to move), and a light bulb converting electrical energy into light (doing work).

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