Work and Power: Lever Efficiency Problem

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Homework Help Overview

The discussion revolves around a physics problem involving work and power, specifically focusing on the efficiency of a lever system and the application of forces at angles. The original poster expresses confusion regarding the calculation of work done when a force is applied at an angle, as well as the interpretation of given information in the context of their homework constraints.

Discussion Character

  • Exploratory, Assumption checking, Conceptual clarification

Approaches and Questions Raised

  • Participants discuss the calculation of work done using the formula W=fd, questioning whether to consider the angle of the applied force. There is an exploration of how to apply the concept of efficiency in a lever system, with one participant attempting to isolate variables in the efficiency equation.

Discussion Status

The conversation is ongoing, with participants providing feedback on each other's reasoning. Some guidance has been offered regarding the correct application of the angle in work calculations, and there is a recognition of the need for clarification on the efficiency problem. Multiple interpretations of the problems are being explored, indicating a productive dialogue.

Contextual Notes

The original poster mentions a tight timeline for learning, with multiple units to cover in a short period, which may contribute to their confusion. There is also a concern about whether the problem contains extraneous information meant to mislead.

NDiggity
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Homework Statement


A person uses a rope to pull a 1000kg. boat 50.0m along a wharf. The rope makes an angle of 45 degrees with the horizontal. If a force of 40.0N is used to move the boat, how much work is done?

Homework Equations


W=fd
Here is my problem. My physics class has 5 days left and we have 3 units to get through so were basically doing a unit in a day and a half. So my teacher is giving a very brief overview of the units and then gives us work sheets. So I am still a little confused. Is the question just giving me extra information to trick me? My question is, if the direction of movement is horizontal like in this question, do you use the horizontal force to find work then? Do you only use the tension in the rope if it is given to find the force needed to move the box horizontally.

The Attempt at a Solution


I'm not too sure. I thought maybe it was 40(50)=2000J since 40N is needed to move the boat 50m.
 
Last edited:
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You are close but not close enough. Remember that the rope makes an angle with the horizontal.
 
is it 40(50)cos45? I'm obviously still a little confused with this unit since we had to learn the whole thing in a day.
 
NDiggity said:
is it 40(50)cos45?
That is correct.

The work done by a constant force is F.d, the dot product of the force and displacement. In the problem at hand, the displacement is purely horizontal, while the force has both horizontal and vertical components.

Here's a site that you might find helpful, http://hyperphysics.phy-astr.gsu.edu/hbase/wcon.html
 
correct:biggrin:
 
Thank you very much for the help! I have one more question.

A force of 2250N is exerted on a lever system to raise a 1200N rock 1.32m. If the efficiency of the lever is 58.7%, how far did the effort force move?

So I used the efficiency equation: Efficiency=work with no machine/work with machine

I plugged in the variables to get:
58.7=1200(1.32)/2250d

I isolated d and got .012m. This seems too small. What did I do wrong?
 
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