Question

Calculate the final velocity right after a 119 kg rugby player who is initially running at 7.45 m/s collides head‑on with a padded goalpost and experiences a backward force of 18500 N for 5.50×10−2 s

Answer 1

Mass of the rugby player = m = 119 kg

Initial velocity of the player = V₁ = 7.45 m/s

Final velocity of the player = V₂

Backwards force on the player = F = -18500 N

Negative as the force is acting in the direction opposite to the initial velocity of the player.

Time period = T = 5.5 x 10^-2 sec

The impulse of the force is equal to the change in momentum of the player.

FT = mV₂ - mV₁

FT = m(V₂ - V₁)

(-18500)(5.5x10^-2) = (119)(V₂ - 7.45)

-8.55 = V₂ - 7.45

V₂ = -1.1 m/s

Negative sign indicates the velocity of the player is in the opposite direction of the initial velocity of the player.

Final velocity of the player = -1.1 m/s