The Change In Gravitational Potential Energy?

[Scray XXI]

Homework Statement

A 2.40 kg snowball is fired from a cliff 10.4 m high. The snowball's initial velocity is 19.3 m/s, directed 42.0° above the horizontal. (a) How much work is done on the snowball by the gravitational force during its flight to the flat ground below the cliff? (b) What is the change in the gravitational potential energy of the snowball-Earth system during the flight? (c) If that gravitational potential energy is taken to be zero at the height of the cliff, what is its value when the snowball reaches the ground?

Homework Equations

Gravitational Potential Energy = mgh
or = (mgd)cos(theta)

The Attempt at a Solution

I have concluded that the answers to parts a) and c) are both positive and negative 245 Joules respectively. I am just having a little trouble with part b). I used the (mgd)cos(theta) equation and I also attemped to change its sign and both times I was wrong. This is problem 6, chapter 8 of Halliday's The Fundamentals Of Physics 8th edition.

 

[Scray XXI]

Bump for despirately not knowing how to solve a problem...

 

[sArGe99]

The gravitational force is conservative. The work done by it depends only on initial and final positions of the object.. That should help you a lot.

 

[tnutty]

K + U = K_o + U_o