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
Answer: 0.08 m/s backward
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
Answer: 0.08 m/s backward