A 69.5kg football player is gliding across very smooth ice at 2.15m/s . He throws a 0.470kg football straight forward.

A) What is the player's speed afterward if the ball is thrown at 16.0m/s relative to the ground?

B) What is the player's speed afterward if the ball is thrown at 16.0m/s relative to the player?

1 answer

Solve using momentum
m1u1+m2u2=m1v1+m2v2
u=initial speed
v=final speed
m1,m2 masses

Using the ground as reference,
m1=69.5 kg
m2=0.470 kg
u1=u2=2.15 m/s
v2=16 m/s
m1u1+m2u2=m1v1+m2v2
Solve for v1 to get
v1=2.056 m/s approx.

B)
v2=16+2.15=18.15
Solve similarly to get 2.042 m/s approx.