The rope in FIGURE Q9.4 pulls the box to the left across a rough surface. Is the
work done by tension positive, negative, or zero? Explain.
Work done is positive .
A force pulls the box to the left across a rough surface
Work done is positive when direction of force and displacement in the same direction.
In this case the force and displacement are in same direction so work done is positive.
The gravitational attraction between two objects with masses and , separated by distance x, is , where G is the gravitational constant.
a. How much work is done by gravity when the separation changes from to ? Assume .
b. If one mass is much greater than the other, the larger mass stays essentially at rest while the smaller mass moves toward it. Suppose a comet is passing the orbit of Mars, heading straight for the sun at a speed of What will its speed be when it crosses the orbit of Mercury? Astronomical data are given in the tables at the back of the book, and .
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