Chapter 6: Problem 21
To push a stalled car, you apply a \(470-\mathrm{N}\) force at \(17^{\circ}\) to the car's motion, doing \(860 \mathrm{J}\) of work in the process. How far do you push the car?
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Chapter 6: Problem 21
To push a stalled car, you apply a \(470-\mathrm{N}\) force at \(17^{\circ}\) to the car's motion, doing \(860 \mathrm{J}\) of work in the process. How far do you push the car?
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You're an engineer for a company that makes bungee-jump cords, and you're asked to develop a formula for the work involved in stretching cords to double their length. Your cords have force distance relations described by \(F=-\left(k x+b x^{2}+c x^{3}+d x^{4}\right)\) where \(k, b, c,\) and \(d\) are constants. (a) Given a cord with unstretched length \(L_{0},\) what's your formula? (b) Evaluate the work done in doubling the stretch of a 10 -m cord with \(k=420 \mathrm{N} / \mathrm{m}\) \(b=-86 \mathrm{N} / \mathrm{m}^{2}, c=12 \mathrm{N} / \mathrm{m}^{3},\) and \(d=-0.50 \mathrm{N} / \mathrm{m}^{4}\).
You push an object of mass \(m\) slowly, partway up a loop-the-loop track of
radius \(R,\) starting from the bottom, and ending at a height \(h
A force pointing in the \(x\) -direction is given by \(F=a x^{3 / 2},\) where \(a=0.75 \mathrm{N} / \mathrm{m}^{3 / 2} .\) Find the work done by this force as it acts on an object moving from \(x=0\) to \(x=14 \mathrm{m}\).
(a) Find the work done in lifting 1 L of blood (mass 1 kg) from the foot to the head of a 1.7 -m-tall person. (b) If blood circulates through the body at the rate of \(5.0 \mathrm{L} / \mathrm{min}\), estimate the heart's power output. (Your answer underestimates the power by a factor of about 5 because it neglects fluid friction and other factors.)
You're trying to decide whether to buy an energy-efficient \(225-\mathrm{W}\) \(\sim\) refrigerator for \$ 1150\( or a standard \)425-\mathrm{W}\( model for \)\$ 850 dollars The standard model will run \(20 \%\) of the time, but better insulation means the energy-efficient model will run \(11 \%\) of the time. If electricity costs \(9.5 \phi / \mathrm{kW} \cdot \mathrm{h}\), how long would you have to own the energy-efficient model to make up the difference in cost? Neglect interest you might earn on your money.
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