An 80 - kg quarterback jumps straight up in the air right before throwing a 0.43-kg football horizontally at 15m/s. Sort the following quantities as known or unknown. Take the horizontal direction to be along the x axis. : the mass of the quarterback, : the mass of the football, : the horizontal velocity of quarterback before throwing the ball, : the horizontal velocity of football before being thrown, : the horizontal velocity of quarterback after throwing the ball, : the horizontal velocity of football after being thrown

Given that,

Mass of the quarterback, m = 80 kg

Mass of the football, m' = 0.43 kg

Speed of the football, v' = 15 m/s

We need to sort the following quantities as known or unknown.

1. The mass of the quarterback = known = 80 kg

2. The mass of the football = known = 0.43 kg

3. The horizontal velocity of quarterback before throwing the ball = known = 0

4. The horizontal velocity of football before being thrown = known = 0

5. The horizontal velocity of quarterback after throwing the ball, = unknown quantity and it can be calculated using the conservation of linear momentum.

6. The horizontal velocity of football after being thrown = known = 15 m/s

Hence, this is the required solution.