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Work and Energy Problem


Date: 5/14/96 at 17:10:1
From: Anonymous
Subject: Work and Energy Problem

I am a junior in a senior Math Analysis class in High School.  We are
working on Work and Energy problems in Integral Calculus. However, our 
teacher told us not to use calculus for these problems. Instead we 
should use the formula: 

	        Work = |F||d|cosO (theta)
where theta is the angle betwee F and d.

I'm having a problem trying to figure out exactly how to do this.  I 
can't seem to find what angle I should use or what to plug in where.  
Please help!

Question:  
The mass of a loaded helicopter is 1500kg.  How much energy does 
its engine expend in ascending vertically for 120m?

Thanks a lot.


Date: 11/12/96 at 21:46:24
From: Doctor Robert
Subject: Re: Work and Energy Problem

In this case the angle between the force vector and the displacement 
vector is zero degrees.  The cosine of zero is 1 so the formula 
becomes:

  W = F times d

    = 1500 kg times 9.8 nt/kg times 120 m = 1.764 x 10^6 joules

In a different type of problem, one might have the displacement vector 
in a different direction from the force vector.  A simple example of 
this is pulling a box along the floor by attaching a rope to it so   
that the rope makes an angle of 60 degrees above the horizontal. In 
this case the displacement is horizontal, but the force is not.

-Doctor Robert,  The Math Forum
 Check out our web site!  http://mathforum.org/dr.math/   
    
Associated Topics:
High School Physics/Chemistry

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