
Energy
Activity Answers
 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
 The same model
has a velocity of 2.2 m/s. How much kinetic energy does it have?
E_{k }= 1/2(m)V^{2} = (1/2)(1)(2.2)^{2} =
2.42 j
 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)U^{2}
 A fullsized 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
 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)V^{2} = 1/2 [(4.900 + 825)/9.8](35^{2})
= 357,813 j
 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
* 10^{9 }j
New Vel. = Old + Change = 35 + 132 = 167
m/s
 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 B17 Flying Fortress.)
