PHYSICS WEP Problems-Set 2 W = Fd = Fd cos 0 PE = mgh KE = 1/2 my2 P = W/t PEel = 1/2 kx2 W = APE = AKE 1. A 220kg refrigerator is dropped from the top of a 42m tall building. A) What is the refrigerator's potential energy just before it's released? PE = MGH = 7 PL = ( 220KG ) ( 9.8m / 3' ) ( 42m) PE= 905 525 B) What is the refrigerator's kinetic energy just before it's released? KE = 1/ 2 mv 2 KE = 1/2 ( 220 kg ) C) What is the refrigerator's potential energy just before it strikes the ground? PEtnigh D) What is the refrigerator's kinetic energy just before it strikes the ground? E) What is the refrigerator's speed just before it strikes the ground? RE ENY / 2 MV 2 7 2 KE = VZ m 2. A bike rider approaches a hill at a speed of 8.5 m/s. The mass of the bike and rider together is 85 kg. The rider coasts up the hill. Assuming that there is no friction; at what height will the bike come to rest? BASE S APE soirD ni Town T info side ! comale esvom 3. Tarzan, mass 85 kg, swings down on the end of a vine from a tree limb 4.0 m above the ground. How fast is Tarzan moving when he reaches the ground? P=W/FKinetic Energy (KE): is called the energy of motion."- -. . 4. A skier starts from rest at the top of a 45-m high hill, skis down a 30 incline into a valley, and continues up a 40.0-m high hill. Both hill heights are measured from 0 203 17 - 69 - W the valley floor. Assume that you can neglect friction. (Hint: Conservation of Energy problem) A) How fast is the skier moving at the bottom of the valley? W= APE = AKE B) What is the skier's speed at the top of the next hill?arei andw (a W = KK thenoginotordi ei tedW () 5. A 200-gram (.200 kg) bullet is traveling at 650 m/s. It strikes and embeds in a tree. You measure that the bullet travels 5.85 cm (meters?) into the tree. What average net force does the tree exert on the bullet? (Hint: W = AKE and yes, the tree does work on the bullet) W= AKL 6. Lake Point Tower in Chicago is the tallest apartment building in the US. Suppose you take the elevator from street level to the roof of the building. The elevator moves almost the entire distance at constant speed so that it does 1.15 x 105 J of building? work on you as it lifts the entire distance. If your mass is 60.0 kg, how tall is the PE= mgh h: DE/mg7. A screech owl, mass of 1.15 kg, is sitting on a branch 4.25 m up in an oak tree. She sees a mouse scurry across the ground and makes a dive for it. Assume that the owl glides; does not flap her wings,and n WE PE A) How fast will the owl be traveling the moment before she grabs the mouse? B) If the mouse ducks into a hole and the owl misses, how fast will she be going just before she alights on a branch 2.5 m up in a cedar tree? 8. Santa has just put presents under Sam's Christmas tree, but he still has a rather large bundle slung over his shoulder. He is carrying a 125 kg load of presents and he needs to take them back up the chimney. A) How much work will Santa do to get the bundle up onto her roof, a height of 6.5 m? W = FD B) What will be the potential energy of Santa's bundle on her roof? PE = mgh 9. Koen and Barrett are testing their catapult. They pull back on the bungee cord, spring constant of 525 N.m, a distance of .475 m. How much elastic potential energy is stored in the stretched-out bungee cord? PEC : 1 / 2 kx 2