A 1.50 kg snowball is fired from a cliff 12.5 m high. The snowball's initial velocity is 14.0 m/s, directed at 41.0 degrees above the horizontal. (a) How much work is done by the gravitational force during its flight to the flat ground below the cliff? (b) What is the change in gravitational potential energy of the snowball-Earth system during flight? (c) If the grav. potential energy is taken to be zero at the height of the cliff, what is its value when the snowball reaches the ground?(adsbygoogle = window.adsbygoogle || []).push({});

For (a), I have used

Wg= mgd (cos theta) to get Wg = (1.50 kg)(9.8 m/s^2)(12.5 m)(cos41), and arrived at -.987 J/m.

For (b), wouldn't this be indeterminate? I thought we needed a reference point for y to calculate the change in gravitational potential energy.

For (c), I used U-Uinitial = mg(y-yinitial), and arrived at -183.75 J. My reasoning is that the change in potential energy does not depend on choice of reference point for the snowball on the ground (at y=0), so instead it depends on change in y. Therefore, we get change in U = (1.50 kg)(9.8 m/s^2)(0-12.5 m)=-183.75 J.

I think I am getting caught up and confused in physical properties, etc. Please help if I am wrong or please let me know if I am correct in my reasoning! Thank you so much.

Gin

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# Homework Help: Potential Energy Problem!

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