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stackptr

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## Homework Statement

A weight is suspended from a spring 50 cm long and stretches it by 1 cm. Take the other end of the spring in your hand and rotate the weight in a horizontal plane so that the spring is stretched by 10 cm. What is the velocity of the weight? (The force with which the stretched spring acts is proportional to the amount of its tension. Disregard the force of gravity when the weight is rotating.)

## Homework Equations

F

_{s}=F

_{g}=F

_{c}

kx = mg = mv

^{2}/r

Where F

_{s}is the spring force, F

_{g}is the weight of the body, F

_{c}is the centripetal force, k is the spring constant and x is the elongation of the spring.

## The Attempt at a Solution

mv

^{2}/r = kx = mg

v=√(gr)=√(g*60cm)=2.42 m/s.

But the textbook says the right answer is 7.7 m/s. My problem is I can't determine k, the spring constant, and what to do next. Also, the problem says to ignore the force of gravity. Doesn't that mean that we assume the mass has 0 weight?[/SUP]

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