Yahoo Answers: Answers and Comments for Physics spring problem? [Physics]
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From Brandon
enUS
Fri, 09 Oct 2015 13:21:04 +0000
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Yahoo Answers: Answers and Comments for Physics spring problem? [Physics]
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https://answers.yahoo.com/question/index?qid=20151009132104AAr7XLt
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From NCS: a) Potential energy gets converted to spring e...
https://answers.yahoo.com/question/index?qid=20151009132104AAr7XLt
https://answers.yahoo.com/question/index?qid=20151009132104AAr7XLt
Sun, 11 Oct 2015 10:44:06 +0000
a) Potential energy gets converted to spring energy. If the spring compresses "x," then
mg(x + 0.31m)sinΘ = ½kx²
3.9kg * 9.8m/s² * (x + 0.31m) * sin39º = ½ * 575N/m * x²
which is quadratic in x and solves to x = 0.12 m ← not possible
and x = 0.21 m = 21 cm
b) Spring energy becomes PE and KE:
½kx² = mgxsinΘ + ½mv²
½ * 575N/m * (0.21m)² = 3.9kg * 9.8m/s² * 0.21m * sin39º + ½ * 3.9kg * v²
12.7 J = 5.1J + 1.95kg*v²
v = √(7.6J / 1.95kg) = 2.0 m/s
c) mgΔh = 3.9kg * 9.8m/s² * (0.21m + 0.31m) * sin39º = 12.5 J
The answer should be the same as the LHS in part (b) (the spring energy)  the difference is due to rounding in the value of x. Precisely, x = 0.208218 m.
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