Question

Calculate the final velocity right after a 114 kg rugby player who is initially running at 7.95 m/s collides head‑on with a padded goalpost and experiences a backward force of 17900 N for 5.50×10−2 s. final velocity:/? m/s

Answer 1

Let us consider the direction of the initial velocity of the rugby player as positive.

Mass of the rugby player = m = 114 kg

Initial velocity of the rugby player = V₁ = 7.95 m/s

Final velocity of the rugby player = V₂

Force exerted by the goalpost on the player = F = -17900 N (Negative as it is in the backward direction)

Time period the player experiences this force = T = 5.5 x 10^-2 sec

Impulse of the goalpost on the player = I

I = FT

Impulse is equal to the change in momentum,

I = mV₂ - mV₁

FT = m(V₂ - V₁)

(-17900)(5.5x10^-2) = (114)(V₂ - 7.95)

V₂ - 7.95 = -8.636

V₂ = -0.686 m/s

The negative sign indicates the player is moving in the opposite direction of his initial motion.

Final velocity of the rugby player = -0.686 m/s