.) Beth launches a rocket out in the courtyard. It stays in the air for 7.25 seconds before coming back down.
a.) How high did it get?
b.) With what velocity did it hit the ground upon returning to Earth?
c.) What is its rate of acceleration as it slows down, reaches the peak of its arc, and speeds up as it goes towards earth again?
Lets look at energy:
intial energy=PE at top
ChemicalPE+ initialKE=PE at top.
but it had no initial KE, so
ChemicalPE=PE at top. Now that energy was released when it fell.
so curiously, chemical energyinitial=mgh
then when it falls, mgh=finalKE
This is exactly like free fall, with an initial KE=FinalKE.
so then 7.25sec /2 is the time of fall.
h=-1/2 g t^2 solve for h at top.posted by bobpursley