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Chapter 9: 9.Q. 9 (page 227)
A ball on a string travels once around a circle with a circumference of 2.0 m. The tension in the string is 5.0 N. How much work is done by tension?
Work done by the tension is zero.
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Hooke鈥檚 law describes an ideal spring. Many real springs are better described by the restoring force , where q is a constant.
Consider a spring with .
It is also.
a. How much work must you do to compress this spring ? Note that, by Newton鈥檚 third law, the work you do on the spring is the negative of the work done by the spring.
b. By what percent has the cubic term increased the work over what would be needed to compress an ideal spring? Hint: Let the spring lie along the s-axis with the equilibrium position of the end of the spring at .
Then 鈭唖 = s.
A 2.0 kg book is lying on a 0.75-m-high table. You pick it up and place it on a bookshelf 2.25 m above the floor.
a. How much work does gravity do on the book?
b. How much work does your hand do on the book?
Evaluate the dot product of the three pairs of vectors in
Figure
a. Starting from rest, a crate of mass is pushed up a frictionless slope of angle by a horizontal force of magnitude . Use work and energy to find an expression for the crate鈥檚 speed when it is at height above the bottom of the slope.
b. Doug uses a N horizontal force to push a kg crate up a -m-high, frictionless slope. What is the speed of the crate at the top of the slope?
The cable of a crane is lifting a kg girder. The girder increases its speed from m/s to m/s in a distance of m.
a. How much work is done by gravity?
b. How much work is done by tension?
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