ACCOUNTING FOR LINEAR MOMENTUM Class 28.1 1. Mass is a state quantity. 2. Velocity is a state quantity. 3. Linear Momentum is a state quantity. 4. Linear Momentum is a vector quantity. 5. Linear Momentum is always conserved. Rat 28.1
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INPUT - OUTPUT + GENERATION - CONSUMPTION
1. INITIAL linear momentum (scalar) for the quantity(ies) of mass in the system,
2. FINAL linear momentum (scalar) for the quantity(ies) in the system,
3. Linear momentum (scalar) of quantity(ies) INPUT into the system,
4. Linear momentum (scalar) of quantity(ies) OUTPUT from the system.
pi = m1v1
pf = (m1v1 + m2v2 + m3v3)
A 1.0 ton (including ammo and pilot) military helicopter is flying at 40 mph. It has a machine gun that fires 60 bullets per second in the forward direction. Each 0.5 lbm bullet exits the gun at at speed of 1800 mph. After a 2 second burst of fire, what is the helicopter speed.
mi = 1 ton
vi = 40 mph
w/ less ammo
mf = ?
vf = ?
FINAL AMOUNT - INITIAL AMOUNT = 0, OR
FINAL AMOUNT = INITIAL AMOUNT
(CONSERVATIVE, STEADY STATE SYSTEM)
Dpwhite = mwhite(vwhite,final- vwhite,initial)
= 2 lbm * (1.5 - 2) ft/s
= -1.0 lbm*ft/s = -0.0311 lbf.s
Dpblack = mblack(vblack,final- vblack,initial)
= 1 lbm * (1 - 0) ft/s
= 1.0 lbm*ft/s = 0.0311 lbf.s