Posted by **Mima** on Sunday, October 7, 2012 at 11:23am.

a block of mass m=0.9 kg is connected to a spring of force constant k= 775 N/m on a smooth horizontal surface. plot the potential energy of the spring from x= -5 cm to x= 5 cm. determine the turning points of the block if its speed at x= 0 is 1.2 m/s.

- physics -
**Erica**, Monday, February 18, 2013 at 12:33am
To plot the potential energy, simply plug your givens into the equation U=(1/2)kx^2. You should get a parabola that goes to 0 in the center.

To determine the turning points of the block, use the law of conservation of energy. You know that Ui+Ki = Uf+Kf since there is no friction. At x=0, there will be no potential energy (Ui=0). A "turning point" is where the motion will stop and the block will move in the opposite direction. This means that Kf=0.

So, set Ki=Uf

(1/2)mv^2 = (1/2)kx^2

(1/2)(.9)(1.2)^2 = (1/2)(775)x^2

Solve for x=.0409 m

This will be the first turning point. The other turning point will be the opposite of this (remember the parabola) - so x=-.0409 m.

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