Work Problems: Calculus Solutions Explained

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The discussion focuses on understanding how to approach calculus problems related to work, specifically involving integrals of force. Key examples include calculating the natural length of a spring based on work done during stretching, determining the work required to lift a cable with coal, and deriving the work done by gas expansion in a cylinder. The fundamental equation for work is reiterated as the integral of force. A suggested starting point for solving these problems is to express force as a function of distance.
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We recently covered work in my calculus class, and I'm confused on how to approach these problems. I know work is the integral of force, but I just don't know how to start these problems. Thanks for the help.

Homework Statement


1. If 6 J of work are needed to stretch a spring from 10 cm to 12 cm and another 10 J are needed to stretch it from 12 cm to 14 cm, what is the natural length of the spring?

2. A cable that weighs 2 lb/ft is used to lift 800 lb of coal up a mineshaft 500 ft deep. Find the work done.

3. When gas expands in a cylinder with radius r, the pressure at any given time is a function of the volume: P = P(V). The force exerted by the gas on the a piston (in the cylinder) is the product of the pressure and the area: F = \pi r^2P. Show that the work done by the gas when the volume expands from volume V1 to volume V2 is: W = Integral from V1 to V2 of P dV.

Homework Equations


Work = integral of Force

The Attempt at a Solution

 
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Start by writing the force as a function of distance.
 
Question: A clock's minute hand has length 4 and its hour hand has length 3. What is the distance between the tips at the moment when it is increasing most rapidly?(Putnam Exam Question) Answer: Making assumption that both the hands moves at constant angular velocities, the answer is ## \sqrt{7} .## But don't you think this assumption is somewhat doubtful and wrong?

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