Unguided weapon canister opening altitude for 4-second deployment

[sroy1313]

An "unguided" weapon is launched off a fighter aircraft flying at 500kts

An "unguided" weapon is launched off a fighter aircraft flying at 500kts (844 ft/s) straight and level at an altitude of 4,000 ft above ground level. The weapon is released from the aircraft with an initial velocity of 10 ft/s (supplied by the bobm rack pistons). The weapon has several selectable canister opening settings controlled by a canister altimeter. These opening settings include 1800 ft AGL, 1500 ft AGL, 1200 ft AGL, 900 ft AGL, 700 ft AGL, 500 ft AGL, and 300 ft AGL. It takes 4 seconds for the canister contents to complete their function. It is desired that none of the canister contents hit the ground before completing their functions. (Note: once the canister opens, the subsystems deploy parachutes, in order to reduce wind drift, it is desired to open the canister as close to the ground as possible, still allowing for the contents to complete their functions.)

a) Select the proper equations to describe the flight of the canister, perform a study to recommend a canister opening setting.


I am unclear where to begin? I know that the first step is to draw a sketch, but after that I am not sure what I am supposed to be looking for?!

 

[grindfreak]

I'm pretty sure all you have to do is solve y = y_0 + v_0t -1/2gt^2 for t when y = 0, subtract 4 sec. and then plug back into the above equation in order to get the maximum time you could have in the air while still allowing the cannister to complete its functions. You could also equivalent solve y = y_0 + v_0(t-4) -1/2g(t-4)^2 = 0.