Hi, Please , take a look at this problem:(adsbygoogle = window.adsbygoogle || []).push({});

A child is trying to shoot a marble of massmin order to hit the center of a box using a spring loaded marble gun.

The marble gun is fixed on a table and shoots the marble horizontally from the edge of the table. The edge of the table is a heighthabove the top of the box. The center of the box is some horizontal distancedaway from the table. the spring constant isk. By what distancexshould the child compress the spring so that the marble lands in the center of the box?.gis the gravitational constant.

In the solution , the manual used the conservation of mechanical energy.( I got this part).

My problem is that I don't understand why they did not use the potential energy PE=mgh

They wrote E_{o}=1/2*k*x^{2}=1/2*m*v_{1}^{2}=E_{1}

They solved for v_{1}, and the they used the projectile equation to find x ( by finding t)

My problem is why for the conservation of energy, they did not write:

E_{o}=mgh+1/2*k*x^{2}

I saw that in other problems solutions tough!

Thank you

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# Homework Help: Marble gun - how far to compress string

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