Energy Problem Set Answers

1. A model glider has a mass of 1 kg. How much potential energy does it have 2 meters off the ground?
   E_p = mgh = (1)(9.8)(2) = 19.6 j
   
2. The same model has a velocity of 2.2 m/s. How much kinetic energy does it have?
   E_k = 1/2(m)V² = (1/2)(1)(2.2)² = 2.42 j
   
3. If the same model descends 2 meters and all it's potential energy is converted to kinetic energy, what is the glider's change in velocity?
   E_k = 1/2(m)U²
   
   
4. A full-sized glider has a weight of 4,900 N, while it's pilot has a weight of 825 N. If it is 1,000 meters off the ground, how much potential energy do the plane and pilot have?
   E_p = mgh or Fwh = (4,900 + 825)(1,000) = 5,725,000 j
   
5. The same glider from Problem 4 has a velocity of 35 m/s. How much kinetic energy does it have?
   E_k = 1/2(m)V² = 1/2 [(4.900 + 825)/9.8](35²) = 357,813 j
   
6. The same glider from Problem 4 has a velocity of 35 m/s. The glider descends 900 meters. What is it's new velocity?
   E_p = Fwh = (4,900 + 825)(900) = 3.63825 * 10⁹ j
   
   New Vel. = Old + Change = 35 + 132 = 167 m/s
   
7. Compare the velocity you calculated in Problem 6 to the speed of sound. Is this answer reasonable? Why or why not?
   167/346 = .48 Approximately 1/2 the speed of sound. (Note: This speed is faster than a B-17 Flying Fortress.)