Here is the question: A women skis down a slope 100 m high. Her speed at the foot of the slope is 20 m/s. What percentage of her intial potential engery is lost? okkk.. here is what I get: My instructor mentioned this was a Ef/Ei problem. (effientcy final divided by effientcy intial) my book uses the formula: 1 - (KE2/PE2) Im confused where the one came from? then... I understand we have PE at the top of the hill only being we are to assume she is at rest... so no KE. So does that mean we no PE at the bottom only KE... Im confused.. can someone explain this to me in laymens terms so I can rework the problem. Is there an easier way to solve this.??