A large fake cookie sliding on a horizontal surface is attached to one end of a

Question

A large fake cookie sliding on a horizontal surface is attached to one end of a horizontal spring with spring constant k = 390 N/m; the other end of the spring is fixed in place. The cookie has a kinetic energy of 19.0 J as it passes through the spring's equilibrium position. As the cookie slides, a frictional force of magnitude 12.0 N acts on it. (a) How far will the cookie slide from the equilibrium position before coming momentarily to rest? (b) What will be the kinetic energy of the cookie as it slides back through the equilibrium position?

Explanation / Answer

Cookie does work against friction and to stretch the spring

Conservation of energy

19 = Forcefriction x d + 1/2 kd^2 = 12d + 1/2 (390) d^2 solve for d ( a quadratic I'm afraid)

195 d^2 + 12 d - 19 = 0 d = 0.26 m


As it slides back, 1/2 k d^2 = Forcefriction x d + KE

solve for KE = 10.58J

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