To practice problem-solving strategy 9.1 a strategy for conservation of momentum problems. an 80-kg quarterback jumps straight up in the air right before throwing a 0.43-kg football horizontally at 15 m/s . how fast will he be moving backward just after releasing the ball?

Refer to the diagram shown below.

By definition momentum =  mass *  velocity.

Before throwing the ball:
The initial momentum is
P₁ = 0.

After throwing the ball:
Let u = the backward velocity of the quarterback.
The momentum is 
P₂ = (0.43 kg)*(15 m/s) + (80 kg)*(- u m/s)

Conservation of momentum requires that
P₂ = P₁
6.45 - 80u = 0
u = 6.45/80 = 0.0806 m/s

0.08 m/s backward

Jet streams are relatively narrow bands of strong wind in the upper levels of the atmosphere. the winds blow from west to east in jet streams but the flow often shifts to the north and south. jet streams follow the boundaries between hot and cold air. the earth's rotation is responsible for the jet stream as well.